I've got my best 1/8 mile so far with 275/60's and the stock gear ([email protected]) It may be a little quicker with 26" tall tires, but the 28" give consistancy at crappy tracks. The most I would go would be 3.73's, but even that will hurt 1/4 mile with stock heads/cam, even with 28" tires.
I've ran 3.90 gears and 28.5" tires in the 1/8 and 1/4 with no problems. I could run the 3.90's and 26" tires in the 1/8 too, but would have to shift to OD in the 1/4. I've since gone back to the 3.42 gears.