Is that compressed pic on the bumps?
A lower COG is always better for the go fast stuff. My view may be a little skewed since linking the back of mine, but My 36" tires stuff past the fender opening of the glass at full bump.
You probably don't want any more bump travel than when your leaf packs are flat. Negative arc is hard on springs. A lot of the racers let them go negative, but they're having them rebuilt/replaced fairly often.
On the travel, I usually figure out where I want the full bump to be, then figure out how I'm going to mount the longest shocks (within reason) in the compressed length space available. Then what ever droop you get, is what you get.
Hope all that makes sense.
-Dan