The 7750 offers AMD's new VCE which can accelerate encoding functions (such as transcoding when ripping a Blu-ray or recording TV). However, AMD still hasn't released the drivers that expose the VCE logic integrated on the 7000 series cards. So the answer to your question is yes, the 7750 would offer superior encoding performance, but only once AMD releases the drivers.
what have you heard about how VCE compares to Quick Sync? I don't know much about VCE and haven't read anything recently about it, last I heard was that it would be comparable performance to quick sync, perhaps slightly better.