this has me thinkin of getting 390's instead of 410's.....the car currently has 456's in it an 28" 275/60/15 dr's
That's a really minute difference....i wouldn't even bother personally. I'd go all the way down to 3.73. I'm actually thinking about it myself (4.10s and a 5 speed here) simply because i want a more even powerband...not just all take-off and no top end.