Some really good looking and thoughtfully put together bikes here. Without wanting to be overly negative, to me the bigger ones (20") don't look as nicely proportioned as the smaller ones.
I know that this is often true of larger frames but I think it is accentuated by the sloping top tube of the Kona and I'll add, surely to Gump's horror, that I think the same with Rocky Mountains - I will not expand further through fear for my life!
I hope Guy won't mind my stepping just a fraction outside his vision for his thread, as the attached photo doesn't belong to anyone on here. But just to illustrate EdEdwards' perceptive point, here is a Kona with almost no slope in its top tube, because it's in the rather rare size 23.
Although ironically, the owner has his seat quite low and has flipped his stem, so he could have achieved that riding position with a size 19 if he wanted to. He obviously likes a long top tube.
I'm pretty sure the gigantic bike pictured could be one of Barry Wicks' steeds (Kona pro Cyclocrosser) he's six foot four and would ride a largeish frame