Just for another data point, my GTX 460's are averaging about 6 minutes per workunit and claiming 33 credits each. That calculates out to around 55000 WCG/day. I recall during the beta I was getting 55 credits/WU so something has changed there.

If the Radeon 7770 really can do 150k/day then that's likely the card to go with. I'm seeing them on sale here in Canada for as low as $99!