Compared a 2011 64-bit Mac Mini with i7 Snow Leopard (also with no AC supply inside - external DC supply), SSD, 8GB DRAM to:
my older 32-bit 2009 Mac Mini with standard floor-wart supply, Snow Leopard, SSD, 8GB DRAM. Both using Amarra 2.3.2 4319, and stopping all unneeded apps, ala Mach2music.
The older Mac wins. Better high-end extension. More live on Piano and strings. This is what I'm using at Newport Beach show.