I have a PC 7424xp, works fine, noisey as all get out. I recently picked up a Rupes 21. It has the washer mod and a 5 inch backing plate. As has been mentioned, super smooth, relatively quiet and works really well. I have used it with Lake Country Pad and Optimum Compounds and Polish, various waxes. Cars finish out great. I just picked up a Flex 3401. Wow, it works great. Used the same pads and the same Optimum Chems. Works better, on corrections, for me, than the Rupes 21 did. I am eager to try the Rupes pads and chems to compare. The Flex and the Rupes were both very smooth, pretty quiet and both easy to use. The Flex does like to fight and pull on side panels while doing correction work. The Rupes, even with the washer mod, did bog down while correcting side panels. A small adjustment to the tilt and all was good. It also had a big throw for the rear quarter panels on my 993, that is why I decided to get the Flex. Frankly, that is pretty big too, I may just stick with the PC in those areas. They are all nice machines, the Rupes and the Flex are a cut above the Porter Cable as far as smoothness, quietness and vibration. Not to mention, they really cover ground. Good luck. Phil