when driving with a lighter flywheel, just like what chu said, all u have to do to avoid problems when climbing hill is to keep the revs in the powerband. in layman terms.. DOWNSHIFT! even with the stock flywheel, if ur car oledy down to 40kmh and u still try to tekan in 4th gear, of coz it wouldnt go. most of the time we are able to drive up a hill after a great start (momentum) from the flats. so the car's natural momentum helps carry our ride up hill.
once u have to brake/slowdown/stop on a slope and start again, just use a lower gear. in the context of our 4AGEs.. the good parts of power are between 4k to 8k RPM. for a tight hill climb like genting, its best to keep between 5500RPM-8000RPM in a "race" hill climb. how? change down! work that left hand and make sure the needle stays below cutoff and above 5500RPM. its that simple. driving style is the key here. dont believe that crap about light flywheel hill problems / top speed loss.
on a lightened flywheel, u just need more fuel and longer periods of throttling to maintain high speed cruising, bcoz the flywheel's weight and momentum doesnt help anymore. like yoga said, lighten flywheel = rise fast, fall fast. the moment u let go the pedal for something, ur top speed will drop pretty fast too. this lead to the misconception of light flywheel = no top speed. top speed depends more on gearing ratio than on flywheel weight.