I just had a lengthy answer to all three dissapear into the ether. OK, I'm trying again in a more direct route. I'm going to answer each of the questions on a individual basis.
John... I'm not the most experienced tarp camper out there. Last year on the LT I used a Contrail when not sleeping in a shelter or cowboy camping. There was one night where it dipped to about 39F. I was near the top of a mountain, not in the tent, and somewhat exposed to a brisk wind. The bag I use in the summer is rated at 50F, but I'm a very warm sleeper. That was the only night on the thru that I slipped my windshirt over my short sleeved shirt. I also slept in shorts. So 40F under a tarp is no problem. BTW... I'm 68 in two months.
Roger... I guess it wasn't you that I PM about this, so here goes. I am sold on the ID Silcoat Cape after using it on the thru. I used it in heavy showers, raining so hard that the water and mud was above my socks, but the pack and my upper body stayed completely dry. Probably even more impressive to me was the ability to hike on a warm, humid, rainy day and not be stiffled by humidity under the cape. I found that the natural action of using the hiking poles kept the cape slightly out from my body and also circulated air underneath. I can't see anything changing me from the cape, especially when I'd have to carry a pack cover, too. Sorry, no photo wearing the cape.
Dave... I hiked the LT in August. During the day it was in the high 80's in the south and anywhere from 50 to 75 in the north, depending on elevation. At night in the upper 70's in the south to just 40 to 50 in the north. In the north much of the temperature difference was in the elevation varations. Other than the one night when it dipped slightly below 40F while sleeping, the only two times I wore my windshirt were when I was near the top of Camel's Hump and also when summiting Mount Mansfield on chilly and windy mornings. Coming out of the clouds right at the summit of each. I wore shorts all the way and also just a short sleeved shirt except for those exceptions. After the initial 75 miles, almost every day begins with a significant climb. It's enough to warm almost anyone up. I'd say leave all that gear except for the wind shirt and camera, unless you are a very, very cold sleeper. The LT is a great hike. The north is exceptional. Other than the south, let me know if you spot a piece of level ground. In the north it's called "Vermont Flat".