Right now we don't really know the chances for 6 properties. Not for the guaranteed rares and not for the random additional rares. If it is the same regardless of item and monster level, then you can use Blizzard's numbers and the number of elites you kill per hour to figure out what works better for you (assuming negligible difference in repair bills). If there is any effect from monster/item level (especially monster level), then it needs to be thoroughly tested before anyone can say anything.
In any case, since I don't want to invest in more than 1 set (it's just so expensive to have one!) I just get the best non-MF gear I can to try smoothen act 3 farming. It may or may not be the best, but I bet it's better than any strategy that involves keeping more than 1 set of gear. If you go high MF in act 2, sell the stuff you use for act 3 and buy better MF gear for act 2. If you go for act 3 with no/minimal MF, then just stick with it.
Another thing about MF, I'm quite unsure how much it adds in terms of benefit vs cost. Even with items worth >10mil (some much more) I still find myself finding extremely tough packs in act 3 which waste a lot of my time. Investing the gold in MF rather than real stats may or may not end up increasing my loot per hour, since better stats would mean I get stuck on such elites a lot less often. Even with a team (where each member has different packs he has an easy/hard time with) we still find ourselves running into ones that are extremely tough. Besides, finding items with really good stats (aka not massive downgrade) is almost impossible regardless of price - They just don't even show up on the AH too often!