I'll be the first to admit that I'm a slower climber on the Diverge. It doesn't feel slower as it rolls so well but I know it is. I do live in the mountains and I have 38's on it. If I cared,or if I was a lot slower, I'd put thinner tires on but I like the versatility with present setup.
Weirdest thing about the bike is that they scalloped out the seat tube a bit to fit wider tires and keep a shorter wheelbase. Didn't notice it at first. No big deal, but you need to pay attention to how you unclip. If you push your heel in, you can rub shoe against tire. Almost went over a few times due to this. Just have to train myself to push heels out, probably good idea anyway but never had to pay attention to this on other bikes. I don't know if the Diverge could fit 42's as advertised, might just rub the seat tube.