Yes go for lightening, but without slotting, the machine shop you use to lighten your flywheel will know what this means.
There is a HUGE amount of materiual that can be taken off of a std flywheel, the standard 2wd ones weighs 8.9KG when I weighed it, after lightening and a brisk skim to true up it was 6.6KG, 100% safe, I purposely did not want slotting, which is removing the mass of metal that is not used as a clutch friction plate surface between the bolts holes just leaving a web around the outside to locate the ring gear, lightening too much can cause them to grenade, then bits fragment and easily go completely through the car body/bellhousing and anyones legs in the way so a bit dodgy.
Any good machinist knows where to remove, although I can do a diagram if you want.
A heavy flywheel is used to not only help a smoother ilde, but the extra inertia it gives when pulling away makes this easier, you would need to get used to it, when pulling away, it will need just a few hundred more rpm, as having less inertia will slow the engine more readily, but 5 mins to get used to it.
I've had lightened on 8-10 cars and given the choice would always have one, I have one(in me garage) to go on my sapphy when the tired gearbox comes out!!
The std flywheel is VERY heavy as flywheels go, and for £30 going from 8.9 to 6.6, is a massive improvement for the money, and totally safe on a std cossie flywheel, be a good time to fit ARP flywheel bolts at same time.
6.6KG is what I'd expect on a normal car, for a std flywheel it's not partucularly light, this is with ring gear attached, it is possible to get them under 2KG, carbon ones but mega money, and these would seriously upset a road engine.
tabetha