I've been busy lately, so sorry for not replying right away. It doesn't sound like you have a lot of experience with modifying engines (sorry if I'm wrong), so I wouldn't recommend starting out by changing your camshaft. You have to get the engine out (either by pulling it out the top or by dropping the subframe) to get access to the camshaft, and then you have to get it in and out, time it correctly, etc. It's not impossible, but it's definately not a bolt on.
Any cam for any LS engine will fit. I have the 07+ single bolt style camshaft, while you have the older three bolt style cam. If you change cams you'll need to swap out the lifters at the same time, because the DOD/AFM cylinders have different lifters and our cam is ground with a slightly different profile for those lobes (a little more lift). New Era Performance makes a DOD compatible cam, but it is for the G8 GT (08-09) so it has the single bolt style end. That cam is ground with a slightly smaller base circle, so you may want to get custom length lifters to reduce valvetrain noise.
If you change cams, you'll need to retune your engine or it will not run well, if at all. You'll something like HP Tuners or EFI Live; a pre-canned tune won't work.
I can't tell you how much power you'll make, because that will depend on the cam you chose and where it operates best, along with the rest of your combo. In general, you are moving the RPM where you engine makes peak torque when you change cams, and by moving it higher up in the RPM range you make more power at the expense of bottom end torque.
A better place to start modding, and learning, would be (in order) to add a cold air intake, cat back exhaust, Thorley headers or a Hogan downpipe, 1.8:1 rockers, and then either get your intake manifold ported or attempt to swap the LS6 on like I did. After that, you should probably learn to tune your car or get it dyno tuned. That will buy you some get up and go. If you want to go fast cheap, N20 (using a controller and the window switch feature) is the answer. The closest thing to a bolt on is the turbo kit, and it will also buy you the most power.