In my experience (admittedly limited) it's not the size of the tires that holds the road, it's the compound of the rubber. Better tires can make all the difference. When I started riding I was under the mistaken notion that knobby, more agressive tires would hold the road better when things were wet. The opposite is in fact true; slick tires hold the road much better - wet or dry. My hybrid's tires are slick with sipes to channel water away when things get wet and they hold way, way better than the cheap Kendas that came with the bike. Also they are 35s vs. the Kenda's 38s. The same is true for the old MTB that I sometimes commute on; I used to have 26*2.125 knobbies on it, but now I have 26*1.75 slicks and the old girl feels much more sure-footed.

FWIW I like the Jamis Coda for the type of bike you are seeking, but I'm partial to steel. I would ditch the suspesion seat post for a rigid one before I left the store with it, though. It may be a little more expensive than othere bikes you've ridden, but IMHO it's worth a test ride.