The OP explained that his engine is far from stock. Unlike the stock OEM engine where power drops well before redline, the OP’s engine may pull hard right into valve float. His concern about setting a safe RPM, while extracting the investment into his built engine - is real.

The LS650 engine doesn’t have a tach because it isn’t really necessary (and Suzuki was pinching pennies). That’s not true for a built engine. Giving advice like “shift when power falls off” is useless. Redline is set to protect the valve train, it’s not just a line on the tach.

Drag Bike is the one who should comment on this.  

Even though I agree with the "shift when it feels right", I will be installing a tach on my bike.  At times it's not comfortable sitting on both sides of the fence!    

A modern dirt bike can safely rev to 15,000 rpm, but most sign-off around 13,500. Valve float isn’t an issue…the power will fall on its face as you exceed 13.5k.

Yes, you can modify an engine to the point that the engine makes power well into the point where there is valve float, at which point power will fall off permanently. I don’t understand why this is an issue. The OP is making a wise equipment choice for his bike.

Oh, modern MotoGP bikes have EFI. The redline is set by the computer and the rider shifts at the shift light.

IMO, the tachometer is a useful tool, and necessary to protect the engine.  Stinkywheels asked “what is a safe redline?”  I suspect he wants to make sure he doesn’t destroy his engine.
 
Those dirt bikes and moto GP bikes mentioned earlier have rev limiters.  Google “Honda CRF 450”, “Suzuki DRZ400”, or “Husqvarna 701” and you can find where those factory limiters are set.  Best as I can tell, the Savage does not have a rev limiter.  I’ve had mine to 8K several times and it didn’t hit a limiter.  If it has one, the factory set it at well over 8K.

The two most critical concerns are valve float and average piston speed.
 
You never want to lose control of the valves.  Valve float risks a collision between an open valve and the piston.  It also wrecks the valves & seats when the valves crash into the seats because the follower has separated from the deceleration ramp on the cam lobe.  You don’t have to run the valve into the piston to wreck things up.  Smashing valves into the seats does a right fine job of trashing the sealing surfaces and spring retainers.  It also can lead to a snapped off valve (something we see on this forum all too often).

If you want to get reasonable service life, the average piston speed on a street engine should remain below 4500 fpm.  That shouldn’t be a problem on the Savage.  The stroke is 3,701”.  Average piston speed at 7500 rpm is 4626 fpm.  I don’t think anyone is gonna spend much time at 7500 rpm, but it gives you a good reference.  If you want to get good service life from the engine, 7300 rpm will keep your average piston speed below 4500 fpm.

Stinkywheels said he had a “big bore high compression piston”.  If it’s a Wiseco pop-top, there should be a ton of room between the valves and the piston when the piston is at TDC.  If he has a Wiseco flat-top, things are real close.  That “redline” thing starts getting to be a serious concern, especially on an engine without a rev limiter.

The higher gears aren’t nearly as concerning as the lower gears.  In first & second gear, you can bury the tach in an instant.   Folks are also more inclined to practice the proverbial “power-shift” in the lower gears.  Nothing like winding that sucker up to 7500 in first and then missing the shift to second.  Of course, a tach won’t help much in that situation, but at least you will have a better idea of why your motor quit runnin.

The few dyno runs I have done show that the stock engine quits makin power about 5500 rpm.  The available high performance cams start signing off about 6500 rpm, but still make good power all the way to 7K.  There really isn’t any good reason to run it past 7K.  I can’t explain why I constantly do it.  I just can’t help myself.  A quick glance at the tach brings me back to reality.  Whoa!

I also use my tach for speed indication.  I hate taking my eyes off the road to look at the stupid tank mounted speedo.  The tach is a sweet addition.  In fifth gear, 3K = 45mph, 3.5K = 55 mph, and 4K = 65mph.  Helps me stay out of trouble with the local constable.

You don’t need a tach, but it’s mighty nice to have one.

If you have ever watched a Nascar or Indycar race with a camera inside the car, I'm totally amazed that valve springs, bearings etc. can run at max rpm for upwards of 2 hours without exploding. Truly awesome !
Cheers!  
ps: and 12 hr and 24hr races?

So, a million years ago I had a ‘79 XL250 Honda. Great bike, but not much power. At the time, Honda offered a line of parts called ‘HPO’, for ‘High Performance Options’. On the list was a ported head with oversized intake valves, a high compression oversized piston, and a few other goodies.
When the valve cover leak got so bad that I had to address it, I took the opportunity to lose my mind.
I got a round slide Mikuni carb (larger than stock) and pod filter, to replace the Keihin which had corroded it’s mixture screw in place. Then I got a 4” Supertrapp exhaust. Along the the HPO head, I got a Megacycle cam, and sexier valve springs. And the HPO high compression piston brought the displacement to 275 ccs. I was ready to rock!
It took a while to get some bugs out, but when it was sorted out it was awesome.
The bike didn’t have a tach, just paint marks on the speedo for where to shift. With the new goodies, the Motor could go WAY past those shift points. I geared it taller to take advantage of the power increase. With the stock motor, top speed was about 75 MPH. With the breathed on motor, over 85.
One day when I was heading down the highway revving the nuts off the bike (as usual), and there was a loud bang/clunk sound from the bottom end.
I got a truck and got the bike home.
Minor disassembly revealed that the crank main bearings had blown their lunch. I guess the combination of more power and more revs was deadly.
Years later I was reading a bearing book put out by one of the bearing manufacturers, and it stated that if you can reduce a bearing’s RPM by 10%, you can double it’s life. Working the formula backwards, I guess spinning those crank bearings at a few thousand RPMs more than stock greatly shortened their lives.
I was so disgusted by the magnitude of time and money lost, that I put the bike in the local paper for a few hundred dollars, and sold it to the first person who called.
So, the moral of the story is to make the bike work better at lower RPMs, not to raise the redline to the sky.

Then the quoted figures of 31hp and 37 torque are incorrect?