Anything from 54 to 62 with the money being on a 56 or a 58, what's comfy for you will depend on your experience, flexibility and specific dimensions. As long as you can get the right saddle to pedals relationship then the frame can generally be made to work via length of stem. Obviously a really big/small frame will put you at extremes of stem lengths and can have an impact on the handling.
I've been looking at some of the setups for pro riders and there seems to be a lot of sizing down on frames and up on stems. This gives them a more powerful position when climbing and sprinting, more over the front wheel. It does mean shorter head tubes and lower front ends though. So if you size down, but aren't all that flexible, then the drop from saddle to bars may be uncomfortably large. Though you can get angled stems to raise the bars these also reduce the reach.