I have a 2005 Specialized Sequoia Elite size 58. I have a second set of wheels with Specialized Borrough CX --32s. They fit with room to spare. Have to remove a front brake shoe or deflate the front tire to remove front wheel though. I use them for trails, night rides with lights, and winter riding. Its an excellent set up--very versatile. The Borroughs are a little harder to propel--just a little--compared to Specialized All Condition 25s. If you go that route, I would recommend that you consider selecting a slightly easier cassette--perhaps a 12-28 instead of an 11-25.

Regarding drops verses flat bar. I too considered the merits of both. If you're going to ride in the city or other location where you may need to hit the brakes hard--e.g. short site lines at corners, and your rides will be 15 miles or less, then I would recommend going with a Sirrus--if it fits you. It has the cantilever brakes which stop better than the road calipers. Re: fit, I found that the Sirrus has a shorter top bar for its size, typical of hybrids, and would recommend that you be careful and test ride one size up.

One last thing to consider--when I first got back into biking, I thought a 15 mile ride was long. Within the first 4 months riding a Sequoia--I became comfortatable with 45 mile rides. That bike is that easy to ride and comfortable!

Good Luck!