I own a heavily modified 993TT and want to buy the stickiest tires I can put on the stock rims. I am not concerned about how long they last I just want the car to hook up.

I have the same tires that were on the car before I modified the engine and I believe they are too old and have hardened. It is currently putting down over 600whp so it is pretty scary right now with the current tires. It will break all four wheels loose at 90mph!

 

Michelin PS2 is the best all around street tires on the market. They are predictable and grip well both in the dry and wet condition. However, if you really want your car to boost and go without squatting and slipping, you would also need to upgrade your entire suspension as well. I would also run larger wheels like 996GT2 so you can put on 315 tires in the rear.
Love to hear more about your engine built.

 

+1 to what Vincent said except 996GT2 rear wheels are 12" and won't fit under your 993TT but 996TT wheels will . Please do share with us your engine build.

 

Partial to PS2 as well