By now the artwork size slider is employed, usually, to select a size you like and to fit it as well as possible in the pannel.
So, why not leaving the computer to do the hard work?
Imagine you 'slide' the size and you see that you'd like around 6 albums per row. So, why not having some buttons that automatically reckon the right size and change the slider the way there is EXACTLY 6 albums per row.
Something like that:
And besides, I think it would be really easy to implement.
EDIT: It looks like I didn't explain it well. The button is not supposed to keep this number of albums per row permanently. It only moves the slider, so you don't need to do any kind of fine tuning to fit the albums. Of course, if you change panel's witdth, album's size doesn't change, so the same as now. The button just MOVES automatically the slider the moment you use it to the right point, and nothing more. It's ljust a help. It is not supposed to keep this number of albums per row from this moment on.