The images you show are actually hashing at 680GH not 620GH (For some reason, the Job-Rate is shown less than Nonce-Rate in Bfgminer, you might want to confirm this with your pool).
Yeah you are correct, the pool is showing 680gh/s.
Works great on my Windows 7 machine. Just curious, which distribution of linux are you using? I was trying it on Ubuntu 14.04.1 when I was having those issues. Could it possibly be a driver issue causing it not to work on mine?