FastAl

I've come to the conclusion that I'm running too much tire. Currently I have Hoosier QTP's 28x11.5x15 on some 15x10" Weld Pro Stars. Last year my best time was 12.65@109 with a 1.8x 60'. With this I'm crossing the traps in the low 6000's and want to cross much closer to my 6800 red line. I have heads/cam, 12 bolt with 4.56 gears. But I race at 5800' of altitude so my actual RWHP is more like 330.

What I need to figure out is just what size tire to run now. Based off of a gear calculator I could run 26" high tires assuming my mileage doesn't pick up too much but I'm not sure how much if any faster I would get on the tire. Of course I'm also worried about traction, currently I launch at 6500 and powershift at 6300.

So any suggestions? Would the 27x10.5x15 be my best bet, or could I get away with 26x10.5x15's?