Beside special abilities from items i would agree with all the other who say that the speed is major key who wins.
Who hits first was pointed out several times.
But what I found astonishing is that people start talking of paladins or chevaliers etc or multiclassed F/MU, this means they talk about opponents which have also magical (or clerical or devine) abilities.
But I would favour a true fighter. Only true fighter can achieve grand mastery with a weapon, and this means also they get a decent bonus on weapon speed. A paladin wielding a two-handed sword has a base inititive of 10 (or lets say 8 when wielding a holy avenger ) reduced by 4 if two proficiency slots on 2handed weapon style are spent. A Grand Master gets in addition another boni on his inititive, reducing his offset to 1. This means that in average he hits much earlier giving the mage no free time to cast spells without interruption.
The mage is forced to have protective spells memorized and to cast them, otherwise he is chopped really fast. Thus he has less spells, and the fighter has really good savings a that level...
The mage has no chance. And I believe that most of the other agree, otherwise they would put up parties without chars like korgan,minsc, keldorn. I don't read many post where people suggest to put the mages to the front rank because these mages can easily win most of the battles against normal groups of opponents