Well, I got by with my level ** Hammerdin with around 25%-40% fcr, but really you can make do with none. I would occasionally go with 0 fcr, and it was certainly not impossible, especially if you are doing mf in the pits or mausoleuom, or some other similar easy place. Basically it comes down to how hard the place is that you are mf'ing in, for example I spent most of my time in Chaos Sanctuary, since it had good exp and was just sort of fun, so I would generally throw on a wizardspike in place of ali-baba's blade, thus taking care of resists, mana, and giving me an ample 50% fcr to boot. It's really just all about the minimum you can survive and kill quickly with, and I found it to be worth the loss of 90ish mf from Ali-baba's in order to be much safer and effective. However, if you are doing mainly shenk and eldritch runs, which is my other favorite place, you can really do fine with no FCR at all, since the bad guys aren't too hard, aside from projectile users that often spawn aroudn Shenk. I found success with a few pieces of Tal-Rasha's set, as it gives you added mf, resists, and soem fcr to boot, making it ideal for finding things. Basically though you will just need to find a balance between killing speed, mf, and survival, and that balance will essentially change depending on what area you are in.