If it helps, Im currently running Ableton Live as a send FX processor for a DJM-800 via either a NI Audio 8 DJ or my RME UFX. The UFX has the obvious benefit I can run it much lower latency.
I recently took the plunge and bought the new 2011 MBP17 with 2.3Ghz CPU and immediately noticed that Ableton Live 8 seems to like it rather more than the original i7 thats in my PC. Now part of this cold be that Live (and most of my plugins) simply runs better on OSX 1.6.x than Win7/64, however I doubt that the OS is significant as most processing goes on in DSP code of plugins. Anyway, my new MBP is very respectably holding its own vs a bloomfield i7/930 that has been overclocked to allways run at 4GHz and the PC machine has 1600Mhz memory vs the 1333Mhz memory in the new MBP.
Being a bit puzzled by all this (ie wondering if there was something wrong with my PC) I end up running geekbench on both systems and confirmed that the floating point performance of the 2.3Ghz sandy bridge is in fact noticeably better then my overclocked bloomfield quad core i7.
Certainly everything I have seen so far with this new MBP suggest that these new processors are significantly better for audio processing compared to the previous dual i7 core MBPs.
Yes - the thing gets hot (fans will rev up when running a project with alot of tracks, but thats to be expected when overall CPU use as measured in activity monitor is at 70% or so), no it doesnt freeze or do anything horrible, in fact I have never know ableton Live 8 work as reliably as it has since we have been using the MBP. It also seems to be able to run a 64 track version of the live performance test project at 64 samples (most computers would struggle to run that at any latency) - just left it running for about 30 minutes and all the times we turned it up to check it out - was glitch free.
Nothing special done with the MBP - airport was still active, project running of an external FW800 drive, an external monitor connected (which forces the descrete GPU to be used, which Live also seems to like - gaining about 4-5% cpu uses reduction when the descrete GPU is active).
I dont have a RME UC, instead I have an RME UFX connected to my PC via firewire and to my MBP via USB2 (so I would guess its similar) - if its helpful, happy to run some specific perf tests for you - Have Logic 9, Cubase 6 and Live 8 suite available.