I've got a chro-mo Trek 700 frame and fork (700c rigid similar to what might be considered a CX bike today). I have an almost identical bike set up as a light touring/hybrid/fitness bike and want to set this one up for trails, packed dirt and gravel roads, etc.

My question is about what tire width to pick. My current rims will take up to about 42mm but it seems that most CX and trail tires come in 35-38mm and then there is a jump to 2.0 inch+ MTB tires that would require me to get some new rims. I have plenty of frame clearance to go to bigger tires as the ones currently installed are 42 and there is still a good 1/2 inch on each side and 1+ inch clearance over the center of the tread. The current tires are pretty shot and no longer in production.

I haven't done a lot of off-pavement cycling and never on a 700c so I'm wondering if I should go with 38mm trail or CX tires, or get wider rims and go to a 2.0+ MTB tire.

Input from anyone with experience in trail riding would be appreciated.