How much is too much over gross weight? For example.....the 172 has a gross
weight of 2300 lbs, but what if you are 2345 at time of takeoff.....is that
too much over

Imagine an answer, and then ask how much =beyond= that answer is "too much"?

My answer is that anything over book is too much. It nibbles away at
flight regimes that you might need, and discover too late that you are in.

Jose
--
Nothing takes longer than a shortcut.
for Email, make the obvious change in the address.