Currently I'm running a mixing project using MIR Pro 24 on the new Mac Pro, so I haven't had the chance to really test this using Logic with VI's etc. But I'll let you in on what I've found about using Pro-Tools 11 and MIR Pro. (Notice how everything has the word "Pro" built in these days :P).
So far running Pro-Tools with MIR running in plugin mode using about 20 instrument spots has made a CPU impact of around 35-40% .. which is just awesome :P, means I cnould potenially throw in a LOT more plugin's and even way more spots on MIR. I have the 24 track version of MIR so there's a limit in plugin mode but when I test this on Logic I'll be using VE Pro and I'll be able to have a lot more instruments running via seperate instances of MIR. That review will come shortly.
It's hard to really pin down anything to say about the new Mac .. it runs amazingly, and performance for audio mixing so far has been flawless. I haven't really had that much experience of running MIR on other computers so it'd be hard for me to say whether or not it's faster, punchier than on other systems, but it runs very well. Any changes to the mic positions, settings etc are rendered within a few seconds if not instantly and one is left with the distinct impression of being able to get on with the work, rather than having to wait for the computer to do it's thing while you go make some coffee to pass the time:P
I'm also running a bunch of Steve Slate Plugin's .. Virtual Tape Machine, Master Bus Compressor, (I would be running Console collection and FG-X but both of those are not yet available for AAX 64), as well as Vienna Suites EQ, Multiband compressor, Exciter and Limiter. And of course running some of the AVID plug's like Channel Strip. On the iMac I could not really run too many instances of Virtual Tape Machine without red lining the CPU's (Without running MIR), whereas on the Mc Pro, even with a full session I'm barely touching at 45-50% power .. and that's with MIR running. Making changes in MIR, even loading new room packs while music is still playing works nicely, there's hardly any performance drop, no clicks and pops an the instruments under MIRx make their positional changes with no effort at all.
Summing up this short review, running MIR under Pro-Tools just works exceptionally well. Nice workflow .. no sense of having to wait or to have to read a book while you wait for stuff to load, you can just get in there and get on with your work within a minute of opening up the pro-tools session. Personally I need that, If I get an idea I wanna try out I don't wanna wait 5 minutes for the computer to boot up, Pro-Tools to load and all the data to find it's place. The Mac Pro boots up within 15-20 seconds, Pro-tools and a full session can load within a minute (loading MIR and positions) and I'm off to the races. Under my old system loading the same session, from deciding to turn the computer on, could take upto 5 minutes.
Note: I found that my Pro-Tools was having hanging issues when i first started using it .. I later found that this was because I had one of my Hard Drives (USB3.0) hooked up to a USB2.0 interface .. this will cause severe speed problems, so make sure any external media is connected via USB3.0 or thunderbolt devices only! Kinda obvious I guess .. but sometimes these things happen and we don't know why .. it's awesome when you find out though cos everything works then :P
I realize you all want to know, how this system performs running VI's, VE Pro, MIR and everything all at once .. and I'll be doing that next, in fact later today I'm loading up my film score template (for the project I'm working on) in order to make changes now that it's all on my new Mac .. so stay tuned .. I'll have a performance review of that shortly. But it's safe to say that if you're interested to mixing audio only, with CPU intensive plugs, the new Mac will ace this! No question .. workflow is flawless!