Hi guys,
I'm new to this site though I've been lurking for a few weeks. I'm currently looking for a savage. I've always been attracted by that big 650 thumper motor.But I'm not very fond of custom looking bikes (my background is bikes from the 60's and 70's). But I want to feel that big thumper and the price is very reasonable for a used bike. I plan on modifying the savage in such a way that it will be between a roadster and a cafe. I know the frame is not an ideal start but I'll go from there.

I do have a lot of questions but for the time being, I'll ask only one that will help me in selecting a model .

Should I go 4 or 5 speeds?
Is it possible to drop a 5 speed gear cluster in a 4 speed motor?
Any one can tell me the speed by 1000rpm for each gearbox?
What's the rpm's at 60mph?

Well I guess that's 4 questions!  
By for now.

While it usually is dependent on money available, I definately recommend newer 5 speed vs 4 speed (older). Like me and the other grey haired fools, metal wears with age so for the $1,000. diff between a decade of the savage /ls40 model, get the newest you can afford.
Opinion = prepare flamethrowers.. Don't know about the rpms, actually I no longer care what rpm I am at, i ride a little bit of throttle over lugging, giving me lots of reserve.  I think Tachs are important for bikes with a 500-1500 rpm sweetspot, where you try to stay "in the groove" for maximum control(my old RD350 for example), but it counterproductive on the Savage.
Most importantly, welcome.

"Motorcycle Cruiser" magazine says, "RPM at 60 mph, top gear: 3940".
 Depends on tire size, mine is about 3800rpm with a 140/90-15.  Top speed around 90mph.  Around 1/4 mile 16sec.

Guys, thanks for the info on rpm but I was looking at the difference between a 4speeds and a 5speeds cruising at 60mph. I want to find out if the 5th is really an overdrive.

As to placing a 5speed tranny in the 4speed crankcase, well from the parts fiches, 86 and 95 has the same crankcase set part number . So if the crankcase didn't change, it should be a simple case of dropping the 5speed clusters in with the shift drum and forks.

From 86 to 95 they are listing the same 2 different crankcase sets. I wonder what the difference is between them?
In 1996 and later they are still listing a crankcase set from 1986 but came out with a new number for the second set? Anyone knows the difference?

The differenc between the trannies are very little.   Mainly more gear to play with.  A handy thing when driving thru town.  The Final output ratio are very close.