The OZ's are very light, but the gain you have is from the wheel width (and properly sized tire, 235 on 8"). Assuming the same tire compound, you'd pick up the same performance with a 16x8.
Nothing wrong with a 17" (16x8" are near impossible to find in the SHO sizes) as I run 17x8" to, but the point is where the weight is can be more important than how much.
there are so many variables, it's hard to say "X" and get "Y".
You could have a 20 lb flywheel with 16 lbs of it's mass concentrated at the center, and a thin/drilled outside that's 4 lbs and it's going to take less power/time to spin it to X speed, than a 20 lb flywheel with most of it's weight at the edges, applying the same power as before. In the same vein, lighter tires are more important than lighter wheels, since they are farther away from the axle centerline.
With that being said, the "spool up" effect is going to show itself less and less as you increase gearing, ie, since 1st gear is short and the gearing allows the engine to rev quickly, the inertia effects of the lighter flywheel (or tires) are going to show up more. Less pronounced in 2nd, probably some (very little) in 3rd, I'd venture by 4th gear, with the taller gearing and 100+ mph aero pushing against the car, the rpm climb rate is slowed so much mechanically, that it's not going to really be noticed. It probably shows up on the dyno (in 4th) as the drum spins up faster than a car does pulling from 2000 rpm in 4th to 140+ mph.
Also for drag racing, the alum unit (flywheel) isn't going to have the thermal capacity that a billet steel or cast iron unit would have. I see an alum unit if you are into road racing/auto-x where you want to cut as much (static) weight off the car period, and driveline rotational weight as well.
Since the SHO FW is only a 10" unit or so (material max of 5" from the crank center line) it won't have as much of an effect in a 1st gear pull as a tires (26" tall, max of 13" from the axle centerline) that are lighter. Tires will have most affect, followed by wheels, followed by 2 pc brake rotors since the light part (alum hat) sits right at the axle Also because a dyno drum spins up faster than a car will pull through the same gear on a road w/ aero drag, those things probably show up more on dyno numbers, than real world.
I have a TON of drag passes on my old 89, testing different parts. Going to a 8 lb flywheel over the stock showed no improvement in ET or mph. It was nice for road racing though, where it was easier to blip the throttle and if nothing else it's 13 less lbs (static) on the nose. Probably a bit easier on the synchro's to.
