I will be doing more tests on the 7750 (mainly LAV Video Decoder in DXVA2 Copy-Back Mode + madVR) over the next two weeks or so.
There is a passive model coming up from Sapphire, the Sapphire 7750 Ultimate.
For current usage scenarios, my main concern is the chroma upsampling bug. This is what Hendrik (LAV Filters author) had to say to me in an e-mail exchange:
If you run EVR, it'll use the GPU to upsample chroma, which is dependent on what the driver does. Its been broken before with AMD, and it'll be broken again i'm sure. I wouldn't trust my HTPC with a ATI card for long, their performance is too much driver dependent.
If i had to run ATI with EVR, i would use LAV Video to output RGB, which works around the issue (but has other drawbacks like no renderer deinterlacing)
AMD has excellent hardware, but really frustrating drivers. I am trying to get AMD to address this, but I am not sure whether HTPC performance is really their priority.