Slightly off the essence of the thread, but i drove a helical synchro ppg on a race track and it was really nice, almost stock feel.
I have driven also a dog semi-helical and you do have to slam the gear lever very fast. Quite something, but surely, never for any appreciable road journey, esp in traffic.
I think you really need billet forks for the dog also, and clutch change downshifting to get reasonable miles between rebiulds.
Several people are now fitting straight synch to 1.2.3rd, helical to 4th and stock 5th.
This will be the way for me in my hillclimb StiV3 (if i don't sell it soon
)