Anyways. I would go with the thicker one. I have found that I can use a bag made for cooler temps and be fine. Usually by sticking my feet out. It will work as a top or bottom should you want to change anything around mid hike. This would give you a good warm option as both. You might find on some nights it would be enough on bottom only with no top insulation.
From what I understand from northbounders, you will start off and end in the cold. The middle is going to be really hot. I hope it rains by the time you start.
If it makes you feel any better I just swapped my top quilt for my 15 deg down bag, added my mittens, a second pair of long underwear for use while hiking, and my face sheild. It's freak'n cold out at night now.