My 520 experience
I would definitely go with threadless adapter if you feel the reach is too long. On the road most of your saddle time will be in the drops. Too long of a reach will affect your comfort, especially in your neck and back. As to the size if the standover height works for you, at least 1" clearance to your jewels, the other components can be adjusted. Completely self contained I carry 42 lbs. of gear, any more than that you're taking along too much stuff.
The 520 is a great frame, wheels questionable, changed my crankset to Deore LX, added softride stem and 35 tires.
Changed rear shifter to STI to keep hands on drops most of the time.