I notice a difference between sora and Ultegra(similar to 105 undoubtedly) in terms of the responsiveness of the lever, and the force I can apply. However, I don't see it significantly enough that upgrading would justify the price. If you have a shorter reach than most, Sora is actually Shimano’s only system that allows you to adjust the reach of the levers (not sure if dura ace and 05’ ultegra do, but their levers seem to be positioned better than their older counterparts). You may also want to try different brake pads as well.