I think more important is how a MIDI interface handles SysEx at Windows level, and the only diagnostic tool I know of that will highlight this is MIDITest. Have a read of the section “DirectMusic and SysEx” for an explanation.
The MOTU 8x8s seems to be the only real game in town at the moment but there’s a simpler device by ESI (the M8U XL) which has the advantage of being “class-compliant”, meaning it will work without any 3rd-party drivers on Mac, Windows and Linux. The downside is that class-compliant devices are not multi-client under Windows, but that’s Microsoft’s fault and not the fault of the device. On Windows these devices all show up as “USB Audio Device” which makes it a pain to manange if you’ve got more than one.
After all that I have to say I don’t own any of these devices although I’m thinking about the MOTU MIDI Express XT. It would be great if someone with one on Windows 7 would be so kind as to test it with MIDITest and let us know how it performs 