With the current sale, I just ordered one UL60 and one Pro90 quilt, with the intent to return the one I don't want. I'm thinking the 60 might work in conjuction with a Montbell thermawrap vest (which I'll have along for the night hiking if needed) and a MLD Superlight bivy. My only problem with the UL60 is durability--it will probably only be warm enough for one season of use due to loss of loft. The Pro90, while heavier, might be as warm as the UL60 after loss of loft in a year or two. Ideally, the Nunatak Edge would be great, but sooo pricey.
I'll be doing 65+ mile days, so you might be right about the level of exhaustion requiring a warmer system than the UL60 gives.