If you have a cross bike, you could bring that with two sets of tires and do both. I ride the trails in Burton Creek SP all the time with my SSCX. Obviously, I can't bomb the super technical stuff, but it's doable.

As for riding around the Lake in August, I would avoid it on a weekend. Just too many tourists. Weekdays the traffic should be much better. I usually go clockwise to stay on the lake side, and keep the views a little closer. Plenty of places to stop for food and water so no need to load up. There's not too much climbing but the altitude can be a factor if you are not acclimated. And make sure to wear plenty of sunscreen. Again the altitude means more effective UV radiation.