Any question answered...

Who says? SRAM's claimed weights (which in my experience are usually pretty close to reality) for 10-speed RDs are 178g Force, 188g Rival and 200g Apex. All the specs, including the upgraded materials on the more expensive ones, are on the SRAM website.

They all function the same when new, and you have to go all the way to Red to get the ceramic pulley bearings, which is probably the one bearing on a bike where ceramic is really worthwhile.

Sorry, missed the crucial word 'front' out of that. Force, Rival, and Apex are all listed as 88 or 89g, Red as 58g.