Here's actual run time differences:
3800s with race trim about 6 min. If you let off in corners, about 7 min. Prop=CF48 and 47. Running about 4600mAh with these.
4500s with race trim about 7min. If you let off in corners, about 8 min. Same prop choices. Running about 5200mAh with these.

Not that big a difference. Might get slightly longer also depending on internal resistance. Remember, mAh is what gives you duration. These are FEs, so the longer you run, the hotter you'll get.

Go down in prop might yield slightly longer run times.