my experience some years ago with my 2560x2560 map was that it ran fine on my g3 266 with 160 megs of ram and close to 4000 scenery items and units. it was supposed to have a bunch of models, but never got that far. carl's problem is probably that the level is so huge and in particular has so many high resolution objects taking up memory - and we all know that osx is a huge memory hog regardless of what other apps may be running...
yeah, I guess the greek plugin (if I ever finish!!! hahaha it's taking forever...) is going to be playable in pc's only, and newer models...
but well...what the hell...I don't want to go for less...it's painful but 2560x2560 is the size of the city...