Maybe Speed should not be the only attribute that affects movement distance? Maybe Strength should give a boost to movement distance, and Intelligence a penalty? That sounds tricky to calculate, though.
I wouldn't give penalties for higher stats, that would be a bit strange (e.g. Inteligence - would you think extra carefully before taking a step? ).
But some synergies might be a good idea - e.g. strength might reduce the penalties you receive from armor pieces.
With some decent weapons and armor fighters become quite good, actually. I found a nice sword in the fight with the lighthouse terror, which trivialized fights against most enemies. Movement penalty aside my fighter can tank as well, biggest thread are casters that manage to cast multiple strong spells in one round on him.
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