Just puzzled how this new found ‘stiffness’ manifests itself, considering you’ve got a 26 -29″ flexible disc and about 2.5″ of squidgy rubber between the axle and the ground?
I’m suspicious this is another of those ‘benefits’ invented by the marketing guys that we persuade ourselves we can notice – like stiffer cranks, better Q factor, reduced seal stiction…
If you ever go from a very flexy frame to a pretty stiff one, you can definitely notice less twang in the rear end of the bike. I.e. it goes where you point it slightly more accurately. Whether that’s enough to give you a real-world speed increase probably depends on loads of factors especially confidence level.
It’s one of those things like posh dampers, good coffee and expensive hifis that you can train yourself into understanding, and you forever need to spend more money on.