Price-cut timing could explain much of the spread. Two homes may both sell after 112 days, but one may have been realistically priced from day one while the other found a buyer shortly after a reduction. If possible, note the date and size of each change rather than only the final marketing period.
I would not settle on a contingency percentage yet. A large reserve can hide a poorly defined scope rather than control it. Put the quotes into one table showing included work, exclusions, allowances and assumptions for each room.
“Electrical checks” is especially vague: does that mean testing...