I've been reading that you need an i7 processor just to run PT11
http://avid.force.com/pkb/articles/en_US/Compatibility/Pro-Tools-11-System-Requirements
from the link:
Desktops
Supported
Mac Pro mid-2012 5,1 (all models, all speeds)
Mac Pro early 2009 (all models, all speeds)
Not Supported
Mac Pro 3,1 "Harpertown" models and lower
Laptops
MacBook Pro & Air
MacBook Pro Retina 15-inch (Mid 2012: 10,1)
MacBook Pro Retina 13-inch (Late 2012: 10,2)
MacBook Pro 15-inch (Mid 2012: 9,1)
MacBook Pro 13-inch (Mid 2012: 9,2)
MacBook Air (mid 2012 models)
MacBook Air (2011 models)
Mac Mini
2012 Mac Mini (all models, all speeds)
2011 Mac Mini (all models, all speeds)
Mid-2010 Mac Mini (all models, all speeds)
iMac
2012 iMac i5 (all models, all speeds)
Mid-2012 to Late 2009 i5 & i7 (Unibody)