My symptoms were huge, embarrassing plumes of black, chunky smoke (especially when cold and when accelerating) and even worse gas mileage than normal. I'd already replaced the O2 sensor, plugs, plug wires, cap and rotor, and other things I'm not remembering. It still smokes a little when starting (more gray than black and I'm taking a break from troubleshooting for a while), but I averaged around 20 mpg on a road trip down I-5 after replacing the regulator. Usually I get around 15-16 driving around town, but got as low as 10 with the bad fuel pressure regulator. We do as many repairs as possible ourselves, but went to a German car specialist to test why all the black smoke. If I'm remembering correctly, it was spraying about 40 PSI more than it should have been. After replacing the regulator, I replaced the O2 sensor and plugs again because they were really gunked up from all the carbon going through the system. I'm guessing that the cats are probably full of crap as well, all the more reason for my son to build me a new exhaust system.
By the way, new plug wires made a big difference in the acceleration and overall smoothness when running.