Sorry guys I'm a late bloomer to this site so I probably missed the consensus on what tire brands/model we should be using the 08 GT's? I have 20" rims.

 

I have had both Nitto 555's and Hankook V12 Evo's on my car in size 275/40-18.

If you are looking for an inexpensive tire that still performs well, I would definitly look into the Hankooks. While I believe the Nittos gave me better maximum dry traction, they were sloppy and miseable in the wet. The Nittos could be pushed to their max holding force, then completely let loose. Whereas the Hankooks on the other had tend to grind into corners slightly, but are very predictable when they are pushed to their limits and they are awesome in the rain.

Just a couple options to consider