I run a lot of ECR enduros (SEDiv series) at VIR, Charlotte and Daytona. They are 90 minutes with a mandatory 5 min pit stop + pit lane transit time (around 20 seconds depending on track). At those tracks a 1.6 will go the distance without refueling, without short-shifting - running wide open. I've done it both ways, refueling to start lighter, and filling the tank to eliminate the need to get out of the car. Dave W. is right, no refueling is the easy fun way. F1 teams ain't watching my results. A lot can happen during a long race and pit-stop f-ups can happen too.
When I fill the tank all the way I jack-up the left side of the car and bounce it to burp air bubbles.