I have the GA-Z77-DS3H and i7-2600k. 10.7.4 + BH 5.0, and I ran some tests.
The drive is a WD My Passport 1T, and it shows up in xbench as WD My Passport 0730. Speeds were about 60% faster than USB 2. I think that's typical for an older 2.5 inch portable drive.
A Seagate GoFlex 1.5T portable was about 60% faster than the WD on sequential tasks, but same on random. Same drive through FW800 on my laptop was about 1/2 the speed of the USB 3.0. So USB 3.0 is over 2x fast as FW800 for this drive.
I don't have any desktop USB 3.0 drives.
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