To Quote Hellhammer specs,
"1199$ 21.5" iMac
Intel Core i3-2100 (3.1GHz)
AMD 6490M with 256MB GDDR5
750GB HD
2x2GB RAM; option for 4x2GB
1499$ 21.5" iMac
Intel Core i5-2400S (2.5/3.3GHz); option for Core i5-2500S (2.7/3.7GHz)
AMD 6750M with 512MB GDDR5
1.5TB HD; option for 3TB
2x2GB RAM: option for 4x2GB
1699$ 27" iMac
Intel Core i5-2400 (3.1/3.4GHz)
AMD 6750M with 512MB GDDR5; option for AMD 6950M with 1024MB GDDR5
1.5TB HD; option for 3TB
2x2GB RAM; options for 4x2GB, 2x4GB and 4x4GB
1999$ 27" iMac
Intel Core i7-2600 (3.4/3.8GHz)
AMD 6950M with 1024MB GDDR5
1.5TB HD; option for 3TB
2x4GB RAM; option for 4x4GB"
More is here
https://forums.macrumors.com/threads/943495/