So, I have a Rupes, a GG 6, and a PC. I think a GG6 is the most universal machine of the bunch, due to it's power and the ability to use pads 3-6.5". It also has the power to correct glass with the correct pads and glass polish. I bought the GG6 after I had the PC and it was a major upgrade for me.
If your interested in the Rupes, IMHO the machine will work best with THEIR pads and polishes (at least their pads), so to get the full benefit of the Rupes smoothness - factor in the price of pads. I think the Rupes system is a no brainer - if you can afford all the goodies. But, you will still need another machine to use 3-4" pads with. You can use your PC there, but I'm not sure how well it would work with Rupes polishes.
I had the chance to try a 3401 at DF at the Flex booth. I wanted to see about the machine "walking". Well, after a few seconds the machine seemed familiar to me. It does take a bit more "control" than a Rupes to use, but I think I could buff out a car with a 3401 no problem.
There has been the occasional 3401 user that posted they have had trouble finishing on certain paints for whatever reason. This may be do to the direct drive of the machine - or maybe just the user. But, the 3401 does have a lot of power and can use pads as small as 4".