Originally Posted by
MassiveD
That bike is nuts for what you are trying. You can do the whole trip which I gather is a trans-am great divide link-up on 1.5 inch tires.
+1
The Surly LHT is a very popular economical touring choice. It's hard to go wrong with LHT provided it fits you. A DT adds disc brakes at the cost of about 4 additional pounds to the complete bike. Having owned both, it is a noticeable weight increase to the unloaded bike.
A compromise is to get a LHT, ride it a lot, then if dissatisfied with braking swap in a geometrically-identical DT fork, disc capable front wheel and mechanical disc brake. This will provide ~75% of the (mostly wet weather) braking advantage of the DT for 50% of the additional weight. If you get a 64cm LHT in black, then the DT fork would color-match if you decided to get one several years later.
WRT wheels on a LHT/DT, know that you will not roll any faster on 700c(28") than 26" once loaded. I think a 64cm will probably look better with 28" wheels. However, 26" wheels (with rubber) are usually a little stronger/longer-lived and lighter than 28", and you can fit a wider 26" tire on a LHT vs 28" for off-road use(2.1"/53mm vs 42mm tires WITH fenders).
Finally, if you get a LHT/DT, be sure to get one with an uncut (350/400mm 700/26) fork steerer tube. Since you seem to be in a hurry, if you buy a Complete LHT, then inquire regarding steerer tube length before transaction so you'll know what you're getting. Framesets are sold with uncut steerer tube, but some of the Completes sitting on the LBS floor have had a bit of the steerer tube cut off for appearance sake.