Well, the plot thickens. If your compression rings are good enough to give you 150 or so PSI, then I can't see how enough oil is getting past them to cause the fouling you are describing. even if the oil control rings were gunked up, the compression rings should take care of most of the oil on the cylinder walls. The oil control rings are there to keep most of the oil away from the top or compression rings where it won't be exposed to the heat of combustion and turn into a carbonized mess. I'm starting to think your rings ain't in such good shape afterall. Try a new set of plugs, see if this eliminates the rough idle. Set your trip odometer to zero and see how long it takes for the roughness to return. If new plugs don't smooth things out, then something else is causing the problem.
1987 BMW 325