Whats the biggest street cam I can use?

The biggest cam that you can use is the one that doesn't drive you crazy.

I have used a purple Hyd. cam @ 292/.509 and it drove me nutz!

While currently, I am running a Comp solid cam that is about 6* larger and more lift and I like it a lot.

Run a cam with the duration that fits the RPM range your driving in with as much lift as you can stuff into it.