kenesis maxlight frame, sizing opinions?

hi, im thinking of re-building the components from my current steed (Trek
6500) onto a spanky kenesis maxlight frame, my biggest dilemna however is the sizing of the thing.
My current frame is a "large size" which measures about 19.5" center to top , while this feels
comfortable I think that a little more clearence might be preferable (the trek has a non
sloping top tube) , The kenesis size I had in mind was an 18" center to top , with a 554mm top
tube. The next size up on the kenesis is a 19.5" which would obviously be the same as my trek.

Im about 6' - 6'1

What size could people recommend?