No matter what you do the throttle won't open much beyond 70%, that's pretty much WOT for these things, unless you go FT flash, which is a waste of time on stock turbo.
I'm sure there are many technical differences but from what I've seen on "other" forums there doesn't seem to be a whole lot of a difference when it comes to the end product. Either way you'll get about the same psi. I think the biggest reason people go with the new pump route is simply so they don't have to worry about messing up the installation and I believe they come ready to go, no break in procedure.
There's the actual throttle position and accelerator pedal position; the first is useful info, the second isn't.
You're still going to want to go easy for the first 100 miles or so on a new pump install, too. There's some fine tolerances in there.
Pressure is not the be all and end all of a pump install, the unmeasured component is volume. If you look at the pictures of the slugs in a CDFP stock for aftermarket, you can see a huge increase in volume per stroke as well. THIS is what primarily keeps your modified engine together, NOT just high pressure. You need the high pressure, too and this is hard to do, as pressure and volume are pretty much inversely proportional in a FP. This is why we can't use a regular electric gerotor pump in this car. For DI, it would have to be the size of a big can of tomatoes to move the volume required and still produce the pressure required and would suck the life out of the electrics of the car to run it.
