I just checked my Verbatim 250GB USB 2.0 2.5" HD (which Debian informs me is actually a Samsung) with the latest Buildbot and tried comi.
No problems with the portable HD itself. There never was before in USB 1.1 mode anyway.
I don't compress my files. I played up to the end of the first scene with Wally. There was a small jerk just after the difficulty selection but apart from that up to the end of the first scene had no problems for me.

   

To summarize, just in case there's any confusion left:

To use USB2 in ScummVM, you need:
a) HBC >= v1.0.8 running under IOS58
b) a nightly build of ScummVM/Wii, the released v1.1.1 is limited to USB1, even with IOS58

The IOS HBC uses is chosen by the HackMii Installer, not by HBC itself. The installation contains this information, and that's a prerequisite set by Nintendo's infrastructure. So IOS58 needs to be installed at the time you run the HackMii Installer. It will print out which IOS it has chosen for HBC before you install anything. You can verify HBC's version and the used IOS in HBC's main menu (press HOME).

ScummVM won't reload IOS, because that would break DVD access.

If that is all given, ScummVM will use USB2. And then you should get similar results like Red_Breast. COMI is one of the most demanding I/O games ScummVM supports. At this time, you will notice some stuttering on the intro, like in one of the first scenes where the map if floating in the air. But this should already be better compared to USB1.

While this isn't perfect, it is the first iteration of USB2 support code. There's still room for performance improvements.

   

MusicallyInspired: MT32 hiccups should be fixed with the next nightly build.

   

Thanks, I'll try it out when it comes.

   

Next nightly build contains some USB2 improvements. I/O throughput doubled (in my tests, 3MB/s -> 6MB/s). COMI intro is almost perfect now

   

Excellent!