I spend some time thinking about buying a new machine. I use an iMac i7, late 2009 model for work and gaming and I love it. Apple didn't manage to anounce a new one so I upgraded my machine with a SSD and a new graphic card. Wait, a new gfx card - usually not possible on an iMac. Well, Apple used very similar layouts for 2009 up until 2011 models so the 2011 card fits into the 2009.
You can see the work needed here: http://www.ifixit.com/Guide/iMac-Intel-27-Inch-EMC-2390-Graphics-Card-Update/9553/1