The best option is to find 3 other buddies each with 3 of their own machines. Then you take turns hosting so you get 4 rounds of kills. Even at master 1, you should be lucky enough to get at least one part from each pair of bosses.
If you insist on save scumming then why not just use one machine and kill the bosses. No piece, reload until you finally get it. Then save and use another machine until you get the right portal and get the drops. Save and use the 3rd until you get the right portal and get the drops... That's exceedingly boring though just for a single hellfire ring.
Just do what most people do, turn your normal gear farming run into a key run as well. Make the keywarden a standard part of any farming run because they can also drop other legendary's anyways. The absolute best way is to do these key runs with 3 other people. You're all getting keys at the same time and will all be able to build 3 machines together. Absolutely no more efficient way to go about it than this. You do 4x the work in the same time it would take you to do it solo, plus you get the bonus exp and magic find. --- Dark Souls Youtube channel - Tutorials, challenge runs, pvp and new content. http://www.youtube.com/user/vageta311
A higher master level = better drops. You don't have to go straight to M5 but the higher you can manage the better your chances. As you said, make sure you have 3 stacks of nef valor. --- Guns for show, Knives for a pro
Just do it on master V with friends. It's always better to play in a group. You don't have to provide all the machines and thus you can make more hf rings. --- http://eu.battle.net/d3/en/profile/Motions-2564/ PSN: Mot1ons_NL - add me for D3 online
Are the stacks of Valor necessary for keys to drop or do they merely improve the probability of keys dropping? --- Men have what I call a Columbus complex: other people may have been there, but we still want to feel like we discovered it.