While this is not quite the answer you be looking for...
The 2011 Mac Mini Server, is in many ways the better bet for use with Logic because...
It has a 2.0Ghz i7... so slightly slower than the 2012 models..but it is the i7 version with 8 Cores.. so it still flies..
It comes with 2 x 500GB 7200rpm Hard Drives built in (Compared to 5400rpm Drives in the 2012 model)
Memory easily upgraded to 16GB for about $90 via Amazon..
..and yoi get a free copy of OS X Server, if should wish to use it at some point in the future... (The MMS comes with the Standard OS X installed and you have to run the add on server program to install OS X server so if you don't need the server stuff, don't run the Server installation software and you'll be running standard OS X as normal)
USB2 instead of USB3 is about the only other important difference that matters for AudioExt Drive use but using the FW800 and Thunderbolt ports, via Tbolt to FW adaptors on the 2011 MMS removes the need for USB3 I find..
Othert than that the 2011 and 2012 models are pretty much the same...
But.. the real kicker is that Apple are currently selling refurbished ones (with full warranty) at $759..... down from $999 originally...so they are quite the bargain..
http://store.apple.com/us/product/FC936LL/A/refurbished-mac-mini-with-lion-serve r-20ghz-quad-core-intel-core-i7
I bought two of these originally and have never regretted it.. So much so that i just picked up another as a spare...
Got to be worth consideration... and at that price.. You could buy two... and use Vienna Ensemble Pro 5 to sync them together..
A Basic Guide to VEP5 and Logic info that i wrote, can be found here...
http://www.logicprohelp.com/forum/viewtopic.php?f=5&t=78956http://www.logicprohe lp.com/forum/viewtopic.php?f=5&t=78956
...add a screen and still save money conpared to buying a mid level iMac.... and you would be getting one **** of a punchy system for your buck.
Other than that suggestion..
In regards to the original question... Always go for the i7 models as hyperthreading adds 4 more (virtual) cores and that can really make a difference in performance compared to the 4 cores of an i5...