Hi,
I have a macbookpro mid 2009, intel core 2 duo, 2.53 GHz. 8 GB, but I run Mainstage in 32 bits due to the overprocessing induced by the audio bridge.
I have a Motu ultra lite MK3 to which we connect 2 guitars, one bass, one cavaquihno (brazilian samba guitar), the lead vocal mic, and for certain songs we use up to 6/7 playbacks. We play west african electro music, so a lot of mixing between acoustic and electro sounds.
When the sono enables it, we use all the outupt of the MK3 to send the tracks to the sono guy.
We don't have midi keyboard, only a FCB1010 foot controller connected to the midi in of the MK3.
So far, no CPU or Ram pb. We are at 40%. But it is also clear that u have to know how to optimize the use of the plugins and to settle your concert project.