I'm not sure if you have done this but I would check the following:
1. Check fuel pressure at idle and make sure that it rises 1psi for ever 1psi of boost. Drive around with the gauge and look to see if you have any strange pressure drops or changes while cruising and in your rough spot.
2. Use rom raider to log the roughness monitors on #1,#2,#3,#4. Look at the roughness while at idle in real time then give it a little throttle, make note of a cyl showing more roughness then the others. Try cruising and watching this. If you can isolate it to a cyl you may consider swaping that injector then the coil pack. I have run into issues with faulty or leaking injectors as well as coil packs causing your problem.
3. Swap the front O2 sensor again with a known good one. You mentioned when you disconnected the rear sensor your problems stopped. Thats fairly odd. Try disconnecting the front sensor and see what happens. The car usually uses the front sensor to trim the fuel, it responds very fast with short term fuel trims, when the front sensors start to go bad a classic symptom is what you described. You may be able to spot a sudden trim if you log rpm and af correction #1 if there is a sudden swing in fueling this should show it. Try to log as little as possible to keep the definition high in the logs.