You're all forgetting that the pump is driven mechanically by the engine. Whilst the standard pump can supply fuel for 360hp at 6000 rpm, at 3000 rpm it can only make half that. (Or thereabouts)
On a K03, going stage 2+ allows more torque and more grunt below 4k rpm. Above that I couldn't really notice a difference. Not the same bang for your buck compared to a K04 but it's certainly not a waste.
I'm still not quite understanding the logic, the pump is mechanically driven, so say for example at 3000rpm it produces 40bar, as it is mechanically driven it will always produce 40, that is fixed by the pump being driven by the camshaft. Now at 3000rpm the ecu wants 30 bar, the electronic valves in the pump give 30 to the rail, the rest is bled off I assume. Now a stock pump can deliver enough fuel to support a stage 2 k04 at 2000, 3000, 4000 etcrpm, which on stage 2 will produce more midrange and top end power than a k03 in any state of tune, so if it can support a k04 delivering more air everywhere than a K03 how can the same pump not support a K03 delivering less air and thus power and torque throughout the Rev range ?. As jay said he will have a pump producing say 50bar at 3000rpm but the tune will only ever need 30bar for example, which both the stock and updated pump can both deliver. So he's never going to demand more from a new pump than the stock one can produce. all be it on a minute scale a uprated pump will require more pumping force and therefore power from the engine via the camshaft. It will take more power to drive the uprated pump. Prob a negligible loss but we all know what difference turning on the air conditioning pump does to the mpg. But I don't see any reason to use engine power to pump fuel at a pressure you will never use, not to mention the cost of the pump....
It's not peak airflow numbers, you need to look at airflow at a given RPM. The K03 kicks in a lot earlier than a K04, at a part of the RPM range where the pump will/does struggle to deliver enough fuel. With Stage2+ on my K03 i'm able to run more boost pressure at lower RPM (below 4k rpm) than i could at stage 2, as i now have the fuel to go with it, as i can now run 130 BAR of fuel pressure (opposed to 110BAR), as the HPFP can keep up. My baby K03 now runs pretty much flat out the entire RPM range and is very much the limiting factor of my setup.
If you are worried about bang for buck, or ££££ per HP, then no a HPFP is not the way to go. In my opinion, WMI is a much bigger benefit and the kit is half the cost of a Loba HPFP. All depends what you want from your setup, i wanted to max out the K03 as far as possible so i went 2+.
The point i was making is that it isn't a complete waste, but it is only beneficial at lower RPM, as above 4k rpm the airflow demands can be matched with fuel by the OE pump. On a K04 this doesn't happen until much higher in the RPM range, so the K04 is much more compromsied and for a much larger RPM range.
Would be useful if Niki could drop i nto explain as i'm sure he will explain it much better than i can