[Bill Baer]

Well your right, a taller tire does reduce your overall gear ratio but there are to many variables to know if it hurts or helps. For instance it also increases the foot print of the tire so it should hook better.
I have gone from a 4:30 gear to a 3:89 with out affecting reaction time however I also went to a larger motor with more torque at the same time. So I don't have any A-B-A testing data. You could change the gear to match the % change in tire diameter and elimate the difference.
When in doubt test.