fuel, fuel pump question

I've got a '88 Audi 90 4cyl, (manual swap from '89 80 4cyl)

The fuel pump is buzzing really loud. Still works now but I'll replace. What's a better choice to pull from the junkyard: one from a '90 80 4cyl, one from an '89 90 5cyl, or one from a '93 90 V6? Even with the stronger V6 pump, should something else keep the fuel pressure the same and extra flow just get returned? I thought the newer V6 pump was probably the best choice.

Right now the car has some kind of fuel problem. When you go too close to wide open throttle, especially when the gear is too high and rpm's too low, the engines sputters and misses bad. If you drive the car carefully, less than 1/2 throttle, you can get around everywhere with the engine running perfect and only stumbling maybe 5% of the time. Something with the mechanical fuel distributor? Fuel pump not supplying adequate pressure?