My experience is the same as Tom's. The big flywheels are not a liability in an event with a lot of time and distance to get up to speed.
The old British bikes had advantages in power and handling over the opposition most of the time. I lost more races due to stuff vibrating loose, breaking, falling off, etc. than anything else. My preference would be the smoother running setup, either big or little flywheels. A bike has to run at full throttle for a lot of miles to set a record.