For what it's worth, the Kona Jake the Snake comes in a 49 cm, and it has a sloping top-tube, so you'll have more standover. The rule of thumb for cross bikes, at least ones to be used off-road, is to get a size smaller than your road bike. Having said that, this is not a hard-and-fast rule. Your overally height is not as important in this metric as your inseam length.
The Kona frame is very, very nice. It's a little more compliant than the Redline and it has a racier geometry than the Bianchi.
I ride a greatly modded 2001 Kona Major Jake. I love it.