I don't think WoW particularly cares about speed vs latency, but AMD Ryzen chips do - they need speed (without sacrificing much latency). But with your 6700k, I don't think RAM specs matter all that much, so long as you get at 3000MHz.

I think 32GB was the recommended size for BFA, but I'd be curious if anyone testing shadowlands has noticed any signifigant changes in hardware stress there.