i have 4.10s in my 00 auto, i LOVE them!
the slightly higher rpm's will probably keep you running a little slower on the road (ie you wont find yourself cruising at 90mph so much) but thats a good thing.
and YES, get FORD RACING gears. (and supposedly ford motorsport are the same thing). i would definitely pay a few dollars extra for assurance of a factory fit and keeping your rear end warranty.
judging by the installation kit i got from motive (which didnt even get used) they aren't as good of quality as frpp.
my gears cost me just under $400 in the end, not counting calibration.