I wouldn't say the next level up is the GG6. I'd say it's a sideways move is all. It's basically the same machine, same size, same basic correction capabilities.
The difference between the two machines isn't going to shave any considerable time. Your going to find the need to do the same necessary section passes, applying polishes, cleaning pads, changing pads, etc etc.
And the basic processes aren't really any different if you go to a Rupes, or even the Flex 3401. Same processes throughout. There's no way around those processes.
Now the Flex 3401 might shave some better time off a correction, as you're getting much more positive results, not fighting-struggling with a free wheeling machine that is prone to rotation stalling.
But then like the Junkman once said, "This bad boy (the Flex 3401) can and will burn through your paint clearcoat if you're not paying attention and are careful.".
There's nothing wrong with the PC7424XP, it does a fine job, is a well built machine. I might even go as far to say that it's an overall better built machine than the GG6. It just doesn't have the lifetime warrantee that the GG6 has.
A good selection of a variety of a few different size Backing Plates, and the accompanying Pads will help versatility, and make the PC better able to work certain areas. (same with the GG6)
Best way to shave considerable time, is the use of good durable protectants, and good washing habits. This can lessen the need of ever needing to pick up a polishing machine for correction purposes for much longer periods of time.
I first bought the PC7424XP, graduating from a monstrous and boat anchor heavy Milwaukee Rotary Polisher. My next machine I didn't wish to go bigger, but in fact the other way, smaller, to be able to better deal with smaller areas, A and B Pillars, Bumpers, License Plate Coves, Mirrors, you get the picture. So, I bought the little baby Griots 3" DA Polisher.
I wasn't so much concerned with time, but felt I'd rather more have on hand the right tools for the right job.
As I said earlier, an assortment of plates-pads for the PC would be more cost friendly, by not spending hundreds more for another DA Machine, such money could be spent on needed chemical products, and other detailing goods.