I can't comment on how much quantitative difference you'll see between a 7750 and 7790 in the programs you're using, it may not be a ton. I do know that hardware acceleration (OpenCL/OpenGL) is being used more and more in such programs. System power consumption with a 7790 uses 50W idle and 115W load
and the 7790 Bonaire GPU has finer grained power management
so it will theoretically be more power efficient through the entire range of usage (comparatively speaking). At idle the difference would be minimal, so unless the GPU is constantly being pegged in a 24/7 usage, you probably won't notice much difference on your power bill (just turn off a single light bulb somewhere and you'll save more energy). Again....for the same price
If the 7750 is preferable for the lower power usage and you've got decent airflow through your case, this passively cooled 7750
would give the added benefit of silence.
Main: i5-3570K, ASRock Z77 Pro4-M, Asus GTX660 TOP, 500GB Crucial BX100, 2 TB Samsung EcoGreen F4, 16GB 1600MHz G.Skill @1.25V, EVGA 550-G2, Silverstone PS07B
HTPC: A8-5600K, MSI FM2-A75IA-E53, 4TB Seagate SSHD, 8GB 1866MHz G.Skill, Crosley D-25 Case Mod