What do you mean by fixed main character?  You create your own - unless you mean fixed by you having to play a human so the story makes sense.  Framerate was improved (as well as the overall visuals) by a single optimization pass after E3, Bioware dev was talking about it on their forums the other day. 
 
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As already stated, with a fixed voice for the main character, they seem to have gone the Deus Ex route.