After having done some testing myself on the Magneticraft Ore Processing i come to the conclusion:
Bug:
The Railcraft Blast Furnace turns 1 Iron Grit into 1 Ingot which should not be like this - NEI tells me i do need 6 Grit, which would make it even to the IE Blast Furnace. So i am pretty sure this is the bug i accidently exploited for a couple of weeks now O.O
Now since i never used Magneticraft in a non-TFP Environment i have to rely on what i read:
Usually the Crusher turns the Ore into Chunks, the Grinder into Rubble, use of the Grinder for a 2nd time turns the Rubble into Pebbles and finally the Sifter turns Pebbles into Dust.
Now in TFP the Crusher produces Grit which can be smelted right away. If put into the grinder or sifter the grit gets processed but without any more output (with no change made to the Script as OneWolf suggested above)
This way 1 stack of rich ore gives me 29-35 Grits
OR the ore can be put into the Grinder which gives me 32 Pebbles plus 5 Grits (plus a chance for some Nickel Dust) - 32 Pebbles put into the Sifter give me 40 more Grit (plus ~ 2 Nickel Dust) so all in all about 45 Grit
Well what i want to say is ... the usual way Crusher - Grinder - Grinder - Sifter is replaced by either Crusher OR Grinder - Sifter
(since the Crusher yields Grit instead of Chunks, which do not exist in TFP)
Hope this makes sense ... ^^
Okay so we are on the same page and it is just a bug that is causing the issue. With the current configs the IE crusher is more efficient, but based on OneWolfe's comment that will change in a future update. That's good to know. What is nice is I've learned a lot about magneticraft in the last couple days and I have to say I like the mod a lot.
I do remember seeing this bug before. For some reason the Railcraft Blast furnace is just ignoring the stack quantity specified in the scripts and simply processes any item 1 for 1. So I am going to have to add another step to the process and create Iron Ore Lumps from 6 dust or grit and then put those into the furnace instead.