The problem is that we are approaching the flame/burn rate limit of nitro at the rpm we run.
Combined with primitive carburetion the combustion is somewhat short of efficient.

The three main beneficial effects that longer stroke have are- the combustion chamber is more compact giving a shorter flame path, less advance is required and the piston spends more time around tdc to allow for more complete combustion and less fuel exiting the exhaust.

Hence more complete combustion, better power spread and better efficiency/runtime.

The piston also spends less time at bdc so taller exhaust ports are needed for the same time/area.

When will we see bores offset from crank centerline?