I haven't read anything about this, but I have just gone back to NM meph runs and I seem to have passed a RARE item breakpoint. He has dropped 100% rares only so far on about 10 runs. NO sets, NO uniques. MF atm is 303%, we'll see if this keeps up..
Edit: Well, I did ~20 runs, and he dropped zero white/grey/blue/green items. It seems to be past some sort of breakpoint. He did drop 3 uniques, along with the 100+ rares.
@Apis: What wagnala said (charms can get up to 4%MF regardless of size) and congratz on the IST and Valk wing - both great items. Re bringing the ist forward, I'd think twice before doing so, as once its forward you can't bring it backward. You may want to use it in say a Gull dagger if you ever find one.
I did know about the rare breakpoint, but I'm not sure I've ever posted about it due to the fact that most people (myself included) would much rather have sets from NM bosses for the chance of a set amulet. IIRC the best chances of getting a set from NM bosses are at ~125-130%MF. Any more than that and your chance to get sets drops as the chance for rares increase.
Re the ring cubing, its all based on chance. You may find three in 80 tries or none in 200. Your chance per individual attempt is 1:125. I quite like cathans as twinking jewelery - the +str and lifeleach are great for a starting melee character, added resists would just be gravy.