[...]The added grunt comes with added heft of course: much longer cards, and the power consumption is higher (essentially increasing heat output; not so much it would drastically affect cooling, but may increase user discomfort).
Do you know how the "use discomfort" of the HD7850 compares to the HD5750?
The difference itself may not be much, but if you're working in a thermally inadequate environment (high stress, low cooling), every watt counts.
I have used an HD 5770, followed by a GTX 460, and there the difference could be felt. Pulling some reference figures from Techpowerup charts (averages
), the 5770 was 88 W on average and peaked at 93 W (quite close to the 7850 in that regard; 87 and 96 W respectively), and the 460 had a 122 W average and 130 W peak consumption. The 5770 was tolerable to work and even game with, but the 460 was insufferable, fast approaching torture in the summer - it was an overclocked card too, and a reliable review put the consumption figures closer to 140 W. So, a calculated difference of 34 W on average and 37 W at peak was enough to be felt, and a card consuming well over 100 W felt intolerable in my study/workspace in the summer.
As regards to the 5750
and 7850, I would presume the 7850 to be "tolerable" (as above) compared to the 5750, as it does not break 100 W even at peak load, but the difference here is 22 W on average and 26 W at peak, so I think you'll certainly feel it.
My case was the worst case scenario: no airconditioning or mechanical ventilation in the study, so the thermal environment was not only stressed but had poor cooling capacity. I also drove the card hard in gaming sessions and with continuous daily use (HTPC as well as workstation and gaming rig), exacerbating the effect. If you have a cooler environment, you may well get away with a slightly warmer card - but you have been warned!
PS. I have used an Intel iGPU this summer and the difference is remarkable, even to the HD 5770. The study is completely cool, even in the worst summer heat, which has been excellent for working at home and good times with games and movies - both of which the HD 4000 clears admirably, even if not perfectly. Recently played through Spec Ops: The Line even. Only really need the FPS for competitive online gaming.