Seat height and position is critical, too high your pelvis starts rocking. Too low, knees start creaking.
Front of the saddle too high , incredible bag pain!
Off road is a different matter.
I use a Selle Italia turbo titanium saddle for road/ cross and Mtb.
Retrobike forum is pretty good.
I've always worked on the theory of a slight bend in knees on full extension,this seems to work for me as pelvis don't rock and knees are fine. Did ride a bike home for wife which was to small for me so know the feeling in knees from riding to low.
Calling at bike shop sometime this week,he's a real helpful guy, I'll have a word with him.