Just after some tips from some experienced Brau Brewers on how to wring 60L of wort out of a 50L meister...
Possible? Entirely, if it is a medium gravity brew that is to be diluted, piece of cake. See Stux's answer with formulas for calculations.
Wort boil overs?? Nothing to be concerned about if a medium gravity brew. Running at 101 degrees might increase the 'chance' but leaving it at the std 100 (at sea level locations) should be ok. I have started my boil with >65L to no ill effect. The main vessell total volume is about 80L. If you are concerned, keep a water spray bottle handy to knock the foam down. Boil overs seem to occur mostly toward the beginning of the boil before the hot break has had a chance to fully form/coagulate so if they did occur, you probably wouldn't have to guard against them the whole boil.
Fountains??? Never had one. IIRC MHB suggests that the pump break usually takes care of them but you can loosen off the wingnut to allow some bottom leakage until it is sorted then do up again.
Too Much Grain?? There is only so much you can fit in there. I squeezed in >13kg on one occassion (reckon I could have gone a kilo or two more as well) and it was all smooth sailing. It would depend upon the type of grain/grist too; a high proportion of rye could lead to a solid or caked mash grist in which the pumps may struggle to force fluid through. Likewise with a high proportion of flour in the grist. IMO I think wheat has heavier grains, so 1kg of wheat would take up less space than 1 kg of malted barley, therefore how many kg's can I fit in, is a question that may not have a clear answer.
Just hoping for some guidance.... Go forth and make beer. :kooi:
Cheers dudes!