I'm going to guess for a given amount of HP, 2 wheels can be made to go faster.
The lowest rolling resistance can be had with larger tires. Try pushing a shopping cart in the dirt.
The shape to best contain a human and tallest tires is a circle, or close to it.
You would have to add frontal area to cover 4 wheels of the same dia, so you'd have to reduce the dia to get the same frontal area, unless you put them all in line.
Realistically, if the rider is going to balance the bike (not fly-by-wire, 2-wheel steering, with gyro stablization), then the lack of 2 front wheels is a serious safety drawback. Any issue with the front tire traction, and it crashes.
Now you COULD make a motorcycle that won't crash when the front tire slips ...