Hey Nick,
I haven't really loaded the machine down, yet, in terms of running projects with loads of RAM. But I have noticed, in Activity Monitor, that Logic Pro 8 appears to really put the multi-threading to work - all 8 cores run pretty much evenly, most of the time, and only cranking out around 30%, even at the busiest parts of my current score. So, I'm pretty optimistic about performance capacity, looking into the future! ;-)
But I'm afraid I don't have too much to report, at this point. I've got a bunch of overlapping, smaller projects, and there's just no room for any new stuff - soon, I hope. If I do something that really loads this thing down, in the next few days, I'll post a quick report.
cheers,
J.