I did a trip last fall to FATS and then Dupont and Pisgah. Fats has about 40 miles of trails. Do the side with Brown Wave and Great Wall first, it's a blast and flows for ever. You can make it to Agusta leaving after work to save a day if you need, hotels can be had for $50 or so. From there we went to Davidson Campground between Pisgah and Dupont, you could spend weeks there. Dupont has great variety (be sure to hit Burnt Mountain) and Pisgah is incredibly technical (Black Mountain is a must do). Start out at "The Hub" bike shop to get maps and recomendations, they are a class act and have several micro brews on tap for post ride enjoyment. If you can get a full day at each place, it would be worth while, if you have a couple extra, spent them at Dupont.