I have NOT tried it with different boots, but i have ridden the '07 set-up and LOVED it (in short).
What specifically do you want to know about anyway?
Do you want to know how much the flex is sacrificed with standard binding mounts or what?
I do know that the inserts are individually laid in the board and are not a series of inserts arranged along a strip of metal like most boards. This method of insert inlay is an additional reason slingshot initially did not have standard mounting, because the strip of metal alone would reduce flex,
but, in response to riders wishes/complaints the standard mounts were added.
Anyway, aside from the long description, I am guessing that slingshot has done there best to retain as much potential flex energy as possible for those wishing to use other bindings. I am also GUESSING that CWB, hype, or obrien bindings would be the best bindings becuase their base plates do not extend laterally as far out as some of the other companies'
On a side note, maybe you might like the slingshot '08 bindings. seeing as they did alot to please the masses with the new boards, I am sure they did just as much if not more to please riders' feet too. (i wish all wake companies would adopt slingshots on-the-fly binding angle adjustment idea; its so much better than the screw and teeth/ratchet method IMO)
(hope these ideas are helpful even if they do not answer your underlying question)