Just installed lite on 52246 into a Belkin ext usb 2 case.
I'm not clear on this, did you install an internal atapi 52246 into an external usb 2 case yourself? If this is the case, perhaps there is a setting that is wrong and the drive appears to be a usb 1.1 to your computer, because, from what I was told when I was interested in a usb external drive (until my internal drive crapped out and I replaced it in kind, my computer's usb ports are ver. 1.1), usb 1.1 tops out at 4x, despite the drive being capable of much faster reading/writing.
But then, perhaps I am misunderstanding your statement. If you bought it pre-installed in a usb case, it should run at max speed, if you have a usb 2.0 port on your 'puter.
Just a thought.