Some of you may know that I haven't bothered much with MainStage and Logic recently having had a lot of grief with them over the last year.
However, I just discovered some articles written about OS X memory management and the positive impact of disabling the dynamic paging system on a Mac (meaning no more virtual memory). It seems to be the case that disabling dynamic paging is improving the general responsiveness of a Mac very significantly. While some are claiming that it's only good for Snow Leopard, others are saying it works with Lion as well. My experience is that it indeed works well.
Here's a link to an article that talks about the issue and describes how to disable paging. Mileage may vary but I think it might be worthwhile for those who have reported problems with MS and Logic due to overloads to try it out.