I just read 2 cables post.. after I posted my last.. I am going to do an experiment and see what happens.. I'll try the 480 in place of the 9800 and see if 3dmark 11 gives me any better results..Ill be back
Where have you been all these years?
Anyway, back to topic, I suggest you running some actual games (eg free Mafia II Demo) with a built-in benchmark feature instead of using synthetic test.
Mafia II Demo download: http://www.2kgames.com/mafia2/demo/
My slightly oc'ed GTX570, when being helped by a stock 8800GTX and a stock GTX285 as Physx card in Mafia II Demo with everything maxed at 1920x1200, the % fps increases are:-
12.5% and 25% respectively.
So, I do not expect a GTX580 being slowed down by a 9800GT Physx card.
(8800GTX has 128 shaders @ 1350MHz vs 9800GT has 112 shaders @ 1500MHz)
If you have got some numbers, please report them here: