It’s 1/3 for the K20X aswell.
Out of 192 SP:s 128 can be used for 64-bit DP operations ( the other 64 are for ILP found at rutime*).
Since they are 32-bit that yields 128/2 = 64 64-bit ops / cc . Hence the 64/192 => 1/3 .
So it’s no different from K20X. If you check it’s numbers you have 1.3 DP and 3.95 SP => 1.3/3.95 ~ 1/3.
In the case of the Titan I just read that it downclocks in DP mode from ~837 down to 725.
Hence it’s 4500 SP GFLOPS and 1310 DP GFLOPS.
Anyhow, sweet move Nvidia, very sweet!
*Check good ol GF104 which is a less complicated reference