The limbs on all the Excaliburs are the same. The increase in weight comes from the "draw length" or distance the limbs are drawn when the bow is cocked. This is determined by "rail" length.
The 200# bow has a rail that is 2" longer than the 150# bow.
you would get no performance increase whatsoever . the limbs on a 225 lb bow are exactly the same as the ones on a 150lb bow. the draw weight is determined by the draw length