no weight difference...
don't expect any savings by switching brakepads. they all wear "the same" an are within 2g. usually they weigh 11g the pair.
for ceramic rims i'd suggest the green Kool-Stop or green Swissstop pads. they have superior brakepower and won't clog the ceramic surface. you can also continue to use the regular black pads .they have monster stopping power but the heat generated by braking melts the rubber and fills the ceramics "pores" in no time. that rubber soon will make for a shiny brake surface which in dry weather makes for awesome brakepower but once things turn wet the power is gone. so that's basically like braking with a regular Al-rim. but the regular pads last "forever" where the green pads get eaten by the ceramic surface since the rough ceramic surface remains rough unlike the rubberized surface when using black pads. so expect to do 1 full season with regular pads while the green ones need to be replaced more often.
anyway - clean your ceramic rims from time to time with the special Mavic rubberblock. it cleans the ceramic from any debris/rubber that sticks to the ceramic coating.i clean my rims 1-2 times per year and that way they retain their awesome stopping power.