I use aerobars on my fast brevet bike, but not on my touring or rain bike. I'm not on either one of the latter long enough to really make a difference. Touring, the way to go faster is to spend less time stopped, if that's what you want. If you really are going from a 12 to a 14 average, you save 1/2 hr. on a 60 mile day. But I really doubt that difference, unless you are riding upwind the whole way. Aerobars aren't that noticeable until you go over 18, and are a drag rather than an assist climbing.

But if you need them for comfort, that's a whole 'nother deal. They are extremely comfortable, and also much warmer if you are riding in the cold. I use a cut-off speed: I don't ride them at over 30. I also never ride them around serious corners or turns. Safety first.