IMO not worth it....
650 flywheel is marginally lighter. Electrics are old, analog, with straight timing set at the stator plate.
750 electrics have a "timing curve" built into the CDI with a higher rev limit. With the correct CDI (example one from a later SXi Pro) you will have a more aggressive timing curve, higher rev limit, and will feel more power even with the marginally heavier flywheel.
I forget the exact numbers, but I have weighed both, the 650, and 750 flywheels. The 750 is just a few OZs heavier. And then, if you "lighten" the 750 flywheel you are that much more ahead.
If you are able, I would switch back to the 750 electrics.