Yes, I can see how that could be a problem, particularly since there is no way to tell the number of pixels any given screen would have in the slider. Entering the size as text would be the ideal solution for all scale fields, have the graphic slider increment set to something simple like 10% chunks between the common part sizes (0.625, 1.25,..). I feel you on the "<<" and ">>" being gone, they are are huge help.
I probably shouldn't be getting too many big ideas before I really know how the UI works, sometimes the simple things are especially challenging.