I'll let the math majors handle the math.

I started road biking 6 months ago. I started out at 210 pounds and rode around 14-16mph. It's been six months now and I'm 187 pounds and I just completed a three hour ride yesterday at 20.1 mph. I was PUSHING it. It was all flat, along the sea and there was very little wind for the entire ride.

I had been around 17-18mph for awhile and then in the past month or two it jumped to 19-20mph for short rides. Averaging 20mph solo for a three hour ride is an accomplishment - for me.

25mph? Are you kidding? I won't see that for years. To me the power and cardio to get there is astronomical. I can push 25mph for extremely short time periods on flats but can't imagine doing an entire ride like that.

So mabe it's 56% more via math, but in the real world, well, it's impossible! (for me)