Changing to SPDs probably won't change the width, or Q factor of your road bike, because that depends on the cranks and not so much on the pedals. You might want to put shims in your pedals to accommodate that. Also, have you tried just moving your cleat position for the KEOs? It could be more a question of fit (angle and lateral and fore-aft alignment). That said, if you are using KEOs with cleats, some people will have knee problems because of the float (though the opposite is more common--having knee problems with fixed pedals). There are 3 different levels of float that you can try, red being highest, gray in the middle, and black is fixed.