How do you know if your using to much gain?

Just remember the amp you are using has a lot to do with the dynamics of the tone... Some amps you can crank the gain and it sounds like fizzy poo poo, other amps build a lot of character when the gain is cranked high.
 
I just got an 81 set up in an ash-bodied Strat clone with 18V, and I'm enjoying it quite a bit - clean sounds are fine, and I don't need much gain for things to be 'solid'.

Jeff