I never posted any drive speeds at all.   Do you mean interface speeds?   If so, I have checked and I think I have the correct values in bits per second.  I'll forget you confused drive and interface speed if you accept that my spellchecker capitalised the 'b' of Mb and I'm too lazy to spank it? :-)

In theory USB2 has a theoretical max of 480 but I challenge someone to demonstrate that to me. Then again, I think there's still a lot of older PCs with crappy PCI busses out there which might explain why it tends to measure around 300.