We went with the most capable / highest rated towing package from each manufacturer, which determined the axle ratios.
I can see where a numerically higher rear axle *might* provide an advantage in a short sprint. It's much more difficult over multi-mile runs like we did at Davis Dam and in Colorado.
For a relative comparison, see this story I wrote at PUTC. The 4.30 rear axle didn't help against the 3.73.
http://news.pickuptrucks.com/2010/09/rocky-mountain-power-test-2011-gmc-sierra-denali-3500hd-and-2011-ford-f-450-king-ranch.html