What hash rate should I expect using a BiFury with USB2.0 rather than USB3.0?
I found that some USB2 hubs with enough amps (3-4) can take 3 BiFury each easily reaching 5.2-5.6 GH/s. I have 5 running off two 5V 3A hubs daisy chained off of a RaspberryPi with minepeon, works well. You 100% need a couple of fans to keep these cool, I am using arctic breeze, works fine. Errors are at about 4% and temps range from 38 to 50°.

So, the conclusion is… USB2 will work well with BiFury just make sure you have a good amount of amps to supply the thirsty 0.9A they need each! I think they are a good miner for people to get started without spending to much.