I say it depends on what your definition of "max rate" is.

Do you mean max rate that will not significantly shorten the life of the shocks? or max rate that is still within the effective damping range of the shocks?

IMO, the effective damping rate is the more important measurement. While you may be able to run 700lb springs and not cause the shocks to spew oil, I'll guarantee that your rebound will be underdamped, and your compression likely overdamped.

My stance is that your overall performance, not to mention ride quality, will be optimized by staying within the operational range of the shocks. While Koni isn't likely to answer the "max" question, asking them for a recommended range might net you some usable information.