I have toured and ridden both a 700 and 26" bike for years, the 700 a drop bar bike with 28s and the 26" bike a mtn bike with 1.5 slicks. Both ride very well and in this case, the mtn bike with 1.5 slicks steers quicker than my dropbar bike, at all speeds (but that is really more to do wth the frame etc, not the wheel size)
I recently have setup another 26" bike with dropbars , a Surly Troll, with a very short stem, 60mm, with wide tires 26x50mm and with a very similar setup to my 700 dropbar bike, it rides rather the same way. The speed might be a bit lower overall but then that I feel is due to the fact that it is a bit heavier and the 50mm tires are a bit slower than the 28 slicks--but really it is not a large amount, and could be very easily changed by narrower tires. In my past experience, tire choices can change how a bike steers, but that said, I like how the Troll rides.

As mentioned, 26 will give you more room for toe overlap and fenders issues, and one of the bonuses is that a 26in wheel compared to a similarly built 700 wheel is slightly stronger due to teh shorter spokes, but given that you want to pull a trailer, its probably not an issue.