In the end I decided on just the travel blanket. I think it will give me the little extra warmth I might need early on.
It's kind of multi use, can use it in the sleeping bag or wrapped around the shoulders while sitting around and is only marginally heavier then a silk liner. Finally, it's something I wouldn't mind leaving behind in a hiker box should I no longer need it. The down side is the bulk, but it's half that of a second sleeping bag and not a lot more bulk then a COCOON coolmax Travel Sheet.
I might still carry the silk liner. If it gets really hot, I can send the sleeping bag home and just use the liner and blanket.
If we were going into fall instead of summer, the two bags would make more sense. I think a good system would be a 40 degree mummy bag and a 40 degree quit.
I'll let you know if I made a wise choice or not in a few months