Advice needed, leaf springs

Considering thisis the racers forum, what kind of power are we pumping outof the engine?
Calvert racing has a really nice set up for high powered rides.
ESPO.com makes some really nice springs for daily drivers and well prep'd street strippers. I've used these guys before.
Also customizable, overbent 1 inch, 1.5 inch, etc...
Sorry that these places are state side.

Making 580hp, I will be aiming for 650+ with the next engine.