Sorry no help with the 15" vs 17", but thought this may interest some people to give some sense of change between older i7 and the new i7.
Just ran geekbench (32 bit mode as its the trial version) on both my PC and MBP to capture the summary screens.
Basically its a comparison of an 4Ghz i7 bloomfield on 1600Mhz memory with Win7/64 vs 2.3Ghz sandybridge on 1333MHz memory with OSX.
So, obviously the PC wins on integer and memory access performance, though not by as much as you might expect on the integer side.
The MBP however wins by quite a margin on floating point performance.
Ive also been running the live perf test, but multiplied up for 64 tracks.
MBP: 64 tracks - 75% or so in Live CPU meter and about 69% cpu utilization in activity monitor on OSX.
PC: 64 tracks - 70% or so in Live CPU meter and about 50% cpu utilization in windows task manager.
In both cases, the load spread across the available 8 cores seems fairly even, however I notice on OSX it tends to favour the 4 primary cores a little more which I would expect on something fp heavy.
What most sticks out is not so much that the MBP seems to be able to roughly match the PC in terms of plugin within a few points, but that Live seems to get more out of the MBP for the available performance vs what it can get out of the PC. I dont know if this is a processor thing or a OSX vs Windows 7 thing.
At stock speeds on the MBP, then thing swing much further in the new processors/OSX favour.
The best I could do for comparing the GPUs (Radeon 5770 in PC, Radeon 6750M in the MBP).
In general, PC is far more responsive to UI when runnign Live and noticably more responsive in the one games Ive tried. In Starcraft2 on the PC, I run it all at 1920x1200 on ultra and its very smooth. On the MBP, I have to drop it all to medium and its playable at the same resolution, but I wouldnt say perfctly smooth. Become smooth and playable on much lower resolution, but High graphics setttings.
Re heating etc - yes this thing still runs hot under heavy load, and Im sure the fans should be running faster than they are (max out at 5500rpm, whereas alot of people seem to see 6000rpm or more), but it does seem stable and has now had several crash free days of heavy studio use.