| As nelly says the main benefit of the lightweight flywheel is the engine spinning up quicker.
I have one fitted to my 998R.
The only problem i have with idling is when the engine is cold.
Standard flywheel weighs around 6 pounds,lightweight one weighs around 1 pound.
Your 996 has the three phase charging system.
One flywheel i would recommend is from a company called Nichols manufacturing.
Their website is -www.nicholsmfg.com.
Other than that i would rcommend fitting a slipper clutch as well because you will get more engine braking. | 
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