I use Creative's X-Fi ASIO drivers in FL Studio. Are the ASIO4All drivers beter than Creative's efforts? I'm really tempted to get myself a MIDI controller for FL Studio now. Great thread...
I have found creatives ASIO drivers to be unstable, however, if they were as bad for everyone as they were for me, i'm sure they would have improved them.
All in all, ASIO4ALL I would imagine would be the best for performance on non-ASIO cards. if you have ASIO drivers for your card, try those first.