I did the two four bulb fixtures in my kitchen. Took out two big heavy magnetic ballasts (from each light fixture, four ballasts total) and installed a single, fairly lightweight electronic ballast in each fixture. I did have to replace a couple of the bulb holders that broke when I removed the wires from them, and a couple more that lost spring tension (the wires are a push in design on the bulb end connectors)
No more hum, brighter light, about half the current consumption (though I only saved about an amp of draw on each one)
Charles