At the Apple Icon at top left>About this Mac, report OSX version, then click on More Info, then click on Hardware> and report this upto but not including the Serial#...
version 10.7.3
Hardware Overview:
Model Name: iMac
Model Identifier: iMac7,1
Processor Name: Intel Core 2 Duo
Processor Speed: 2.4 GHz
Number Of Processors: 1
Total Number Of Cores: 2
L2 Cache: 4 MB
Memory: 6 GB
Bus Speed: 800 MHz
Boot ROM Version: IM71.007A.B03
SMC Version (system): 1.21f4
On the bottom of your iMac stand, you'll find a label with the serial number printed on it, or from the Apple (?) menu, choose About This Mac. Configure To Order (CTO) models are designated with an asterisk (*). Check the last three characters on the serial number:
http://www.appleology.org/2011/01/how-to-identify-imac-models-from.html
http://en.wikipedia.org/wiki/IMac_(Intel-based)
I think, but do not know, that the latter was simply a Build to Orde model with no significant differences as far as anything goes. 🙂