The i7 Intel processor in the 27" iMac is a ''' 2.8 GHz Intel Quad Core i7-860'''
Uses the '''LGA1156''' Socket
But its the only one in the group that has expanded options available on chip.
'''Expansion Options
PCI Express Revision 2.0
PCI Express Configurations 1x16, 2x8
# of PCI Express Ports 1
''' This is the spec sheet from Intel for the Quad Core i7-860 :
http://ark.intel.com/Product.aspx?id=41316&processor=i7-860&spec-codes=SLBJJ
This site is the Intel's i7 Family Product spec sheet:
http://ark.intel.com/ProductCollection.aspx?familyID=28037&MarketSegment=DT
In conclusion It may be possable to to replace a i5 with the i7-860. but you may not be able to replace a i7-860 with a 3.20 GHz Intel Core™ i7-960 Processor
Kristyanna Virgona