All of the available performance cams have very little valve overlap and they have no affect on how the engine idles - the engine idles and runs smoothly after installation.

The performance cams do add some torque and horsepower - they work even better with the addition of a Wiseco piston to increase the compression.

The available cams are the Webcam Stage 3 available from Lancer in the Marketplace section - or you could try and find a good used DR650 camshaft from the early model bikes.  If you use a DR650 camshaft you will have to drill oil holes in the lobes to use it in the Savage, and I also drill the center hole to match the size of the hole in the Savage cam.

Not necessarily, a cam swap is not difficult if you have some basic mechanic skills.  A piston swap takes a bit more skill and a few more tools, and some more time, but is doable as well.  Many folks here have done both successfully.

This old post will give you a good idea of what to expect when you install a mild cam like the old DR650 cam.  As Dave previously mentioned, you absolutely must drill the oil holes.  Other than drilling the holes, the cam swap is very easy and can be accomplished with common hand tools.

http://suzukisavage.com/cgi-bin/YaBB.pl?num=1626391255

The old post also includes links to modifications to the air box, carb, and exhaust system.  Each old post measures acceleration so you can do comparisons of the before and after performance.  You will be amazed at the improvement.  Up to and including the cam swap, all the mods are low hanging fruit.

You can also find all this stuff in the Tech Section.