I just received my late 2013 iMac 27".
It's a beast! I'm playing Bioshock Infinite on high at 1440p. Not sure about fps... But it runs without problems.
That's my geekbench 3 result:
Http://browser.primatelabs.com/geekbench3/217322
Right now my imac has 8gb ram original from apple. But In a few days I'll be able to post another benchmark with my new memory modules: G.Skill Ripjaws 16gb 1886Mhz CL10
If anyone knows another good way to test my machine, just let me know so I can try and post results later.
Although the results have not been posted in this thread, there are numerous test on geek bench with many different configurations. The iMac had been out for 2 months now.