As for the OP's initial dilemma, I recommend getting the bike that fits, with the added observation that Surly's run big, so test ride one if possible.

On 700c vs 26", in the U.S. I think you will be more likely to find a tire reasonable for touring on pavement in the 700c size than in the 26" size. When I last needed to buy a tire on tour I was in Indiana, and the shop I found (only one in town) had a very limited selection of tires. I was looking only at 700c sizes, but I doubt I would have found a slick 26" tire in that shop.

So if it's a toss up between the 54 and 56 LHT fit wise, then I'd go for the 700c tires if you plan to tour in the U.S.