WRT problems with idle clocks, I had the same problem with my XFX 5770 - it stayed at 500/900 at idle. I then used RBE to check the BIOS and manually changed it to 157/300, and it worked for me with no problem. Other people who has this problem can give a try.
I'd like to report one more serious problem with my HD5770. When choosing YCrCb 4:4:4 pixel format (I want YCrCb because it gives WTW and BTB), the colour is off (I check this via DVE and AVSHD test videos), I think it's probably because of wrong YUC/RGB conversion. This problem doesn't exist in HD4000 series. When I choose RGB 4:4:4, however, the luma output isn't correct. Instead of 16-235, it output something like 16-233. I made a workaround to this problem by adjusting contrast and brightness in Avivo settings in CCC.