You'll be ok on the KATY; the gravel is packed down and not loose like on a backroad. That said, if you have clearance for 28's you'll have a little more stable ride with a little wider tire. Sometimes after a rain you'll come across patches of loose chat and you'll be thankful for them at that point, but I see people riding the trail on 23's all the time. I'll be riding it tomorrow, by the way, and I'll be on 28's.