Gearsets

[Hammer]

Hey Everybody,

I am considering some new gears for the Z over the winter.
What does a person go with, 4:10's or maybe 3:90's, 3:70's.
Any pluses or minuses a person should watch out for when buying them?
Where does everyone buy theirs?
Anything special or different about the installation that would cause a shop specializing in differentials to screw the install up?

I plan on drag racing the car a fair amount so if that's a consideration let me know.

Thanks