I'm guessing that you won't gain much by speeding up. During my BBG in Nevada, I didn't run over 80-82 mph ever except for part of the last leg and then I probably didn't get over 85. Gas mileage suffers so much on the NT when it gets wound up over that that I don't think it would be worth trying to run 90. For my whole BBG, I averaged 42.2 mpg. I had some very high headwinds that pulled it down on a couple of legs, but still got 48mpg on one leg and 45mpg on a couple more. Of course, in Nevada, there weren't many optional fuel stops -- you get gas where you can. The Iron Butt Association also argues in their Archives of Wisdom that higher speeds increase fatigue disproportionately to the advantage gained. That also gibes with my experience. I'm comfortable at 80mph; 90 is not comfortable for me.
My goal was to keep my "moving average" on my GPS at or above 70mph including fuel stops. That would have given me a whole 2 hours and 25 minutes for other stuff. I didn't keep it that high. When I got to West Wendover, a little over 1/3 of the distance, I was down to a 58.7mph average. I was pretty discouraged at that point because I'd been in a lot of rain and it had gotten down to about 35F on some of the passes -- in the early afternoon! I knew that by night, that weather would translate into sub-freezing temps and snow. If the rain had continued till I got to Ely, I was going to bail on the BBG attempt. As it turned out the rain quit and temps did get down to sub-freezing (18F!), but there wasn't any snow. By the time I got to Fallon, just over 2/3 of the distance, I had my average back up to 69mph. During the dark and cold, it dropped some, so that when I left Baker, with 197 miles left to go, I was slightly below BBG pace with an average of only 60.9. It started getting light about 50-60 miles after I left Baker and I felt more confident about getting my speed back up to the 80mph range, although I had some concern about gas. My "out" was a Shell station at Ash Springs, 10 miles away from the station in Alamo that was the finish for the Team Lyle Insanity Rally. If I had to, I could end my BBG there and still get it, even if I wasn't an official finisher of the rally. But I turned out OK, finishing the Rally and the BBG with 12 minutes to spare.
My previous BBG attempt had gone south when I hit two stretches of one-way road with a pilot car in the first 70 miles. At 86 miles into my route, I was 49 minutes behind schedule. When I got to about 1200 miles, I knew I wasn't going to make it. I ended up riding 1430 miles in 24 hours that trip and regretted (later) that I hadn't gone ahead and done a simple BB ride.
The CC50 is still on my horizon -- don't think I'll try a CCC100.
You had a good ride and I'm glad you made the smart decision and stopped for rest!