For mountain biking, you generally do want a little more top tube stand-over clearance than you would if picking a road bike. Three to four inches is probably a bit more than I think is typically recommended. I think one to two inches would be safe. If your top tube really is crammed up against your groceries, and you really do intend to ride the bike off the road and on legitimately uneven terrain, you might need some more clearance. If, however, you think much of your riding will be mostly on the road, then the stand-over clearance on the Jamis might be okay. You could also install shorter tires on it (if it has super large knobby tires on it) for a small reduction in height. Sometimes that makes all the difference.