Update 4
Swapped the fuel pressure regulator this evening and went for a test run. Drove for 90 minutes, nailed the hell out of it... not one blip or problem, no loss of power, and the rear pump didn't get noisy at any point - looks like it's solved
Being a cynical git, I'm going to refit the original tomorrow night and confirm that the fault returns... just to be sure, as I'd hate for the fault to have coincidently gone, only to return when I'm halfway up Stelvio pass in 2 weeks.
Many thanks to all for advice & tips, special thanks to clee for the regulator... let me know how much I owe you and preferred payment method.
Now I just need to fit a new stereo, and maybe try do something with my headlamp lenses (they're the only external part that lets the car down).