PCV is great on our car. I replaced it a year and a half ago and I've only run full synthetic since. There's no positive pressure from the crankcase at all. The engine purrs and hums at 900.
It's exhaust/cat problems for sure. It's all rotted away, there are holes and rust and leaks everywhere. I have a feeling the cat is really bad. I've had two cats go bad before and they sounded similar to this--the instantly loud exhaust noise a specific rpm (on this car it's about the 3Krpm range). If we didn't have that stupid 02 sensor behind the cat I would've just taken off the cat and put a straight pipe back there... But alas!