You must be thinking about aluminum flywheels, this South Bend one I'm referring to uses a steel flywheel and I doubt it's half the weight. I'd be highly surprised if the OEM flywheel is 38lbs by itself.. I don't have to rev the engine any extra to engage first gear with this setup. If there is any extra, it's a very small amount, a few hundred rpms at most..
I've used the FX850 before and that one required to rev it up to around 4k to take off from first gear, so I know what bringing the revs up to engage first gear is like..
I've used the more aggressive FX450 numerous times (about 4 times) in the past and yes it was a bit noisy, but that's due to the single mass flywheel over dual mass one.. That is normal on all performance clutches if you swap over to single mass, not a big deal and totally livable.. might be horrible if you're not expecting it..
Shuddering only happens to if you try and ride the clutch, once you get the hang of it, it's seamless and easy, no shuddering at all..
If an FX250 was too rough for you, you did the right thing and get back to a dual mass flywheel, the FX250 is actually pretty tame when it comes to performance clutches..
I've heard the RSR is a good clutch tho from the folks that use them, just not sure how much power and/abuse it can take or how long they last.
Dual mass doesn't typically like too much torque and the life can suffer which is on of the reasons almost all performance clutches go single mass..