We really go round in circles, don't we?
'Seeley is better because it has no flex!'
'Rickman is too stiff!'
In my experience, neither of these statements is true!
The benefit of a Seeley has shown in tighter corners, the ability to change line at whim! How do you do that with no flex?
The benefit of a Rickman has shown in faster corners, the ability to hold a line at speed pays dividends! Too stiff for what?
The truth is, a rider who has just got off a Seeley thinks a Rickman is too stiff, a rider who has just got off a Rickman thinks a Seeley flexes too much.
It is all about your perspective and ability to adapt!
At some tracks a Norton can finish in front of a Ducati, at others it mostly can't....
BTW. This has very little to do with valve sizes!