This is one of my favorite vids:
I have been using the 3.90 for a couple years, it is much easier to drive around town, but I'm thinking about putting the 3.70 back in.  I think the 3.70 might do better in the 1/4, and I am almost certain it'll do better in the 1mi!
Edit:  This is for GMG:  I'm still running stock config.  In the 1mi, the 3.90 it'll do 171+ in 5th then it needs 6th, which is a complete dog.  With the 3.70, I figure I'll just run 5th and maybe get a better speed.