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.