It's not about the board really, you have to find a 920 that a) likes the 21x mult (only 3 of the 5 I tested like it) and b) one that is a good clocker. Unfortunately even good CPUs may not like certain mults, so it's possible you can run 200x19 at 1,2V but 200x21 remains impossible even at 1,5V
That's the real advantage of the 940 and up, you can pick the CPus favourite mult which makes a huge difference.