I have the 13# Fidanza with essentially stock cams, NO secondaries, with some custom phasing. The idle was run up to 850, and with the new Accel injectors, it is hardly noticeable.
See what you think...
http://www.youtube.com/watch?v=y1YFa8ruh8A
13# aluminum Fidanza:
It is a little trickier to launch at the drag strip, whereas the dual mass stores sooo much energy it is easier to launch, and smoother between gears (does more damping)
inertia dyno indicates the equiv. of approx 15 rwhp when comparing results. (However, the effective rwhp might be significantly higher than that due to the fact the 15 hp value is the effect in 4th gear. The equiv. may be significantly higher than 15 in low gears where the rate of rotational acceleration speed is significantly higher! Just sayin.)
The dual mass:
the dual mass is 46# (vs. 13# for the Fidanza) and makes for a smooth shifting between gears
little or no transmission rattle with stock cams, and much reduced rattle with big cams.
The best of both worlds might be a steel single mass weighing in at around 22-25#. That might be a compromise, especially for LT5s with cams with aggressive phasing.
With good injectors, plugs, and idle at about 850 on a stock cam motor, I don't think there is much to complain about. I like the extra seat of the pants snap, especially in the lower gears!
Your mileage may vary!