I use a cross bike (Spec. Tricross Comp) for rain and riding on dirt/poor roads with 700x32 tires. I like this setup as the bike is quite comfortable on these types of roads and it's quite stable. It's got 105 while my road bike has Dura Ace. I don't notice the difference in the group as far as performance.

In my case, it's not like my road bike couldn't handle poor or dirt roads, but with it only allowing 700x23 tires, it's not exactly comfortable and if the road has a lot of loose gravel, it's also dangerous. The 700x32 tires rolls right over it. I run them at around 70 psi.