light weight flywheels are grand once not over lightened and not ran in a lathed as the balance might be wrong as above ^^^^^ it will run bearings on your crank as its off balance.
pros
free reving, faster take off, a lighter car
cons
stalling on take off, needs more gas going up hill due to loss of momentum, and loss of torque
your choice.. its a turbo so petrol is always going to be a problem as far as loss of torque throw in a decat will take care of that, and take offs probally will always be lively ha ha ha