BCrypt + GTX670 = 6 c/s?

[Rolf]

So yet again, I'm royally fucked, am I?

Kinda.
If you buy several 7970s, you would get 100~150 c/s.
Don't forget, the NV 6xx GPUs are meant for games, not compute, so using 580s or 590s would yield more speed.
Still, AMD gpus are better at this.