Originally Posted by Nevcairiel
They are originally based on the GT114 chip
There is no GT114 chip. Perhaps you mean GF114 (GTX 560), which is based on Fermi architecture, while GK104 (GTX 680) is based on Kepler architecture, a new GPU architecture (based on Fermi Gen2 in a sense).
- T = Tesla (8 and 9 Series)
- F = Fermi (200, 400, 500 Series)
- K = Kepler (600 Series)