ls6
My next 2 mods I did were exactly what you have in mind - LS6 intake manifold and P&P TB. I did the LS6 first and it made a HUGE SOTP difference after 5000rpm to redline. The P&P made the car much more responsive. Both are good must do mods that are worth the $$. Like said about you will probably be sitting with atleast 330rwhp from just these, and 5-10 more depending on how good the tune is.
I don't know if anyone on here has the new design SLP headers yet. I have the American Racing Headers and they are simply amazing. The slid in like butter and the craftsmenship on them is perfect!!
The stock ten bolt can break on stock power, expecially with a M6. So I would stick with street tires until you can afford a better rear.

