I just got a 20* regular wide center zip slick bag. I am 5'10" and weigh 245#, suit jacket size is around 52 to give you an idea of chest size. I have been sleeping in a regular width and length TNF Cat's Meow for several years and it was always snug inside for me, especially around the shoulders. Having the wide in my slick bag is really nice, it gives me room to move my arms freely rather than having to make a concious effort to do so when in the bag. When I stand up in the slick bag the regular height gives me room above my head but when I lay down in it and bend my legs or move around that extra space above my head gets reduced.
So, I would suggest that you go with the long and wide version of the slick bag. You will appreciate teh extra room inside and if it is "too long" you can always cinch the hood down if you want.
I have spent one night in it and slept fine. I was also in a hammock, with a Big Agnes I-Core sleeping pad under me and the slick bag opened up and used like a sleeping quilt. I was nice and warm and the weather got down to at least 33* based on the min/max thermometer another guy nearby had.
Larry