As a general rule. The more the drop, the worse off you're going to be performance wise. Use it loosely though. You're basically gaining performance from lower center of gravity and stiffening the suspension, but losing it thanks to oscillation between the mismatched shock and spring. There is no magic spring rate and height drop that has been proven as of yet on any specific year. And I doubt they'll spend that time doing it because most people concerned that much about performance would have already spent the money to do it the proper way by either matching up a set of shocks or gone full blown coilovers. Not worth the R&D.
"We live for a good time, not a long time."
RIP Colin McRae