So far looks like 700 series has low fps in Witcher, even 600 series beats 700 in some cases. Could be driver issue.

Yeah, game is terribly optimized, you are fine while you play on 900 series, but anything other from Nvidia - it will run just terrible. 100% certainty - Nvidia paid big bag of cash for that, just to sell more 900's. Shame really, downgrade, bad optimization, shady DLC tactics - CDPR is the same as any other company - difference is, they lie about everything better than others.

I play in 1080p, on minimum settings - 30-40fps, my card - 770GTX.

Only thing that can help this game - fire, lots of it