Sizing....the big problem with any conventional sized wheel bike is the wheels themselves. Regardless on it having 700c, 27 or 26" wheels each mandates a minimum crown height which in turn mandates a minimum TT height. The only way around these minimums is to run short sidewall tires which lowers the entire bike or slope the TT. A TT that slopes a total of 4" from the effective will only have a 2" reduction in standover mid tube.
In the early 90's Miyata's 'Elevation' series bikes were available with 13" frames....their TT's where in-line, if not making a shallow 'V' with the seat stay's!!!
That being said, the PDG70 I have has a 28.5" stand over measure mid tube with 26" street tires.