1) number of people in your party
2) number of people in the game
3) number of people in you party and in your area (Chaos Sanct, etc)

MF% does make the odds higher in your favor of getting uniques, rares, and sets. But there is a diminishing returns calculation that lowers your base MF respectively. Blue (magic) mf always remains base (e.g. 300%MF=300% blue mf). If you have 400% MF, then your U/S/R/M MF is about 240%/280%/300%/400% respectively. Once you get to 700%MF, your uniques MF% hits about 275% and tops out at 300%MF at around 1,100 MF. Also keep this in mind - MF has nothing to do with your chances of getting runes.

I once charted the returns for Unique/Set/Rare/Magic and Unique is hyper-exponentially diminishing. More MF doesn't make that big a difference for uniques as 50% more MF means about 1% more unique at this point. But that 1% can make a difference.

For sorcs you have to rely on your merc to kill to get the stacked MF that high, and for babas you have to have dual isted 6-socketed weapons, maxed Find Item, and perfect socketed MF gear with MF charms everywhere. Best I've heard on babas was around 1200+ MF.

But my short answer to your question about rares? By about 600+ MF everything that bosses drop are rare (yellow). Even with 3,000 MF (if that was possible), you still have to hit the Treasure Class first, then get lucky and get a Hydra Bow selected (1 in 6 shot, not bad), and then have it choose to drop unique. In cows, that would be 556,544 to 1. Good luck!

Conner

There can be only One! But there are too many already.

p.s. I once found a Zod rune from a Frozen Terror in Hell, the odds were like hitting a lottery (1 in 1.364 million), so anything is possible.