Pretty much agree with most everything written above. It could have just been your "lucky day", or you may have been expecting too much, too soon, on a relatively lumpy course. However,
- it doesn't get that cold in NC in the winter, so unless you are only targeting the MS-150 once a year, or in combination with a couple other summer charity rides, ride through the winter (you may have to carefully pick your days, and ride in the early afternoons, but riding through the winter will help a lot),
- don't wait until after Christmas to start reducing your weight, Start now. All you need do is eat a little less. Smaller helpings, few helpings. I got above 200 just before doing a Blue Ridge Parkway ride, entire length, north to south, 2 years ago. I weigh approx 50 pounds less now as compared to then.
There are several excellent charity rides coming up soon, including a "Gran Fondo" Oct-13 in Yanceyville (you know that is likely to be a bit lumpy), and (probably) Oct-27, the Durham Halloween Habitat ride will use roads north of Durham and Hillsborough. You may not be FAST on those, but they ought to be scenic and fun.
It is not obvious where you live, but since you did the Tanglewood Tour, I'm going to assume that you live somewhere near Winston-Salem / Greensboro, and since this is the LD, Racing and Rando sub-forum, I'll mention that there are several randonneurs that live over that way, and there are a couple 200-k rando routes available for RUSA members. Beware: some of the randos over Triad way are FAST.
PM me if you are interested in some sorta' local rando info.