You need windows 7 or linux. And elpida memory. Hynix is slower. What card are you using?
Windows 8.1 x64, card- GIGABYTE GV-N970WF3OC-4GD, samsung memory
I believe samsung is hynix based. hynix is in faster copyspeed. Elpida is faster in random acces.
Samsung and Elpida give 20-22MH/s, hynix 17-19MH/s in windows 7. I am not sure about windows 8.1.
You need to get your card to P0 state:
1) open cmd.exe with the admin privileges
2) cd C:\Program Files\NVIDIA Corporation\NVSMI
3) nvidia-smi -q -d SUPPORTED_CLOCKS -i 0
4) nvidia-smi -ac 350X,14XX -i 0 (where 350X is that very first number printed after supported clocks-memory and 14XX one of those numbers printed after graphics)
5) Overclock your memory, +500 generally works. Should give you memory speed of 4005MHz
6) Overclock your core, doesn't make big difference mining ETH.
7) If you wan't to save power, reduce your power limit. Even 60% works suprisingly well.
Someone should open new topic for nvidia and ethereum...