If we're talking about holding a motor flat out on the race track, then a big carb, the right cam & gas flow/turbulence into a big inlet valve will give slightly higher top speed.
But on the street we're probably losing bottom end and mid range to an engine with stock carb, and valves during roll on riding.
The big valve motors were developed for the competition mad american market
Mods do provide some bragging rights
in the bar or carpark for road riders however.
For a quick road motor I would leave carb & valves stock, go for compression of around 8-8.5:1 and fit a 356 or 357 cam and some nice rods that could live with keeping the throttle open. Buts thats just my humble opinion.