If your running stock gearing now and want more power for hillclimbs drop to a 13 in the front. If you change the front it is equal to about 3 in the back.
I love my T5's: the sound, look, and performance. I never had a problem with mine touching the air box. Once I went to k&n pods the only thing that bothered my filters was the airbox mounts so I cut them off.
Rugers are good guns I used to have a p89 9mm and still have several rugers. They work great and are also american made. I would still have the p89 but I sold it to buy a gun for concealed carry, the ruger was just to big. The 2 in the right of the picture are rugers: the top one is a 22/45 and the bottom is a security six 357. The one on the bottom left is what replaced the p89 it is a glock 27 with the clipdraw for concealed carry.