I have GTX TITAN, but performance looks similar (maybe not used DP):

with turned off DP: 485khash/s @ 770Mhz with -l T14x32
with turned on DP: 480khash/s @ 770Mhz with -l T14x32

btw. i don'n know, why clocks are such low with the latest version of cudaminer 18-12-2013, while gaming frequencies are 1045Mhz

If there is some bios editor which can turn off stupid turbo...it would be great :-)