[Johan]

Race drivers were not born with three legs, soooo, when coming down the back straight wide open in 4th gear, the procedure would be to lift off the throttle, put left foot on brake and begin to push, shift to neutral, rev engine up to the rpm level that would match your speed in 3rd gear, then put transmission in third, then lift off the throttle. A good driver can make this look easy, and it is easy, with practice.
Shifting with the clutch still requires matching revs or the transmission "clunks" pretty bad. There are no synchros, just dog gears I believe, same as a Hewland.
If you want to be a race driver, get a Jerico and learn to use it. If you have no interest in track driving, get a street car transmission, in my humble opinion.