I don't believe gas flow is the major issue when comparing single and twin carbs. With a twin carb system the gas in the inlet tract resonates at the same frequency as the exhaust system. In a single carb set-up it resonates at twice the frequency and the branch in the manifold interrupts the column of gas. The difference between the two situations is extremely small but on a race bike, the revs are usually much higher, so there is probably more benefit in a twin carb set-up. The main difference is that a perfectly tuned single carb will give more power than a poorly tuned twin carb set-up. A single carb is easier to get right, because with twin carbs you have to match the needle jets and float levels - so that when you raise or lower the needles, you don't have one side richer than the other. When tuning carbs, the main jets are largely irrelevant as long as they are slightly too rich. The other thing is - of you are doing plug chops to get the mains right - if you fit a bigger main jet and the plugs don't show an increase in richness, you are metering off the needles, not the mains. That is dangerous. If that ever happens, it becomes necessary to recess the needle jets and meter lower down, so that the tip of the needle remains trapped - but the mains do the actual metering at full throttle.
I have never had a four-stroke detonate through have the mid-throttle jetting too lean. When you race, you are usually only on full throttle for a short length of time, but the mixture needs to be a bit richer than what gives best power.
With my bike on methanol, I use 670 main jets. I could probably get away with 620 main jets. But it does not matter - the bike probably has slightly less power for 50 metres of track.