wiring the field & armature in parallel will make the motor slower, and also may burn up the armature. Also I'm not sure that being in series (universal motor configuration) results in the highest possible speed. If you put the armature and field in parallel, and you put a resistor (any resistor with greater resistance than the armature) in series with the field, you would have a seperately excited (sepex) DC motor with field weakening. I think that may be faster, but never tried it, so I'm not speaking from experience.