But was the test "really, really valid"???
Maybe, just maybe ... the driver of the Ford chassis did not (dare - for lack of a better term) rev up the V10 adequately to fully tap it's horsepower???
The V10 is a high rev'er - unlike nearly all other truck engines and unlike most V8's down through the years that all/most of America is "used to". Most V10 RV owners are afraid the motor is going to blow up from, say, 4000 RPM on up ... so they baby it along at lower RPMs when accelerating and/or traveling up grades -> and then wonder-why/complain-afterwards that their V10 seems "under-powered" compared to the thumping truck V8's they've been used to.
I wind up my V10 all the time above 4500 RPM and when doing this it doesn't play Second Fiddle to any other RVs on the road - diesel or gas powered - when going up long haul grades. :B
(Maybe I've been to too many sports car races and/or listened to, or ridden in ... too many high RPM Ferraris?)