Kelly,
ALL the cams currently on the market, from JAPAN were designed for road use. In fact, my guess is if you want a cam for more lower end, you'll have to get one custom ground from someone who knows their stuff.
In fact, until the Kitaco SE series parts came out, all the Japanese motor parts were designed years back for 50cc Japanese Street bikes, and were a carryover to the XR/CRF50's. The SE still has a street cam, but do the the design, pulls like a train in the dirt also. However, Kitaco doesn't use roller bearing cams in their top ends, but do sell a roller cam(s) that can be purchased seperately.
If you want some more roll on power, change around your sprokets (Front - smaller, Rear - larger, or a combo of both) but you'll sacrifice top end.