cudaminer.exe -q --algo=scrypt:2048 -d GTX780 -C 0 -b 512 -i 1 -m 1 -H 2 -l Z12x20 (vtc) -> 335kh/s (and as low as 252kh/s...pretty wild swings but mostly 300+)
I got the strange effect that while Google Chrome is started and visible the hash rates are higher. Does not even have to show a specific web page.
But for now I've stopped mining VTC via p2pool because there is currently a problem with low hash rate workers not getting paid what they should. A fix will be rolled out by VTC p2pool operators soon hopefully.
Christian