2.9GHz Quad-core Intel Core i5, Turbo Boost up to 3.6GHz
8GB 1600MHz DDR3 SDRAM - 2X4GB
1TB Serial ATA Drive @ 5400 rpm
NVIDIA GeForce GT 750M 1GB GDDR5
The bottom line is the GPU spec for the most powerful non-Retina iMac and it is not a 27" model. The GPU is pitiful. Many of the newer 3D games on Steam require a minimum of 1.5GB GPU.