Apple Bootcamp no longer supports Windows 7SP1 on newer iMacs.
You'll be out of luck, Apple don't support older versions of Windows on newer iMacs (no bootcamp drivers). The Bootcamp drivers for a new iMac will only support Windows 8.1/10. Apple no longer support Windows 7 on newer macbooks and iMacs, haven't for a while.
Apple don't support newer versions of Windows i.e. Windows 10 on older iMacs officially, but we have Windows 10 running on a 2008 iMac + 2009 iMac (the 2009 24'' is the one to get). ATI Radeon HD 2600 Pro dedicated graphics are more stable than the Nvidia 8800GS, which freezes occasionally, due to buggy Nvidia Drivers, but the Nvidia 9400M is OK under Windows 10.
Biting the hand that feeds IT
