In person, does plug #1 look very white in comparison to plug #4?
Also, I've heard that oil (on #6) can find it's way above the spark plug. Personally, I've never had that problem, but a DIY on Pelican Parts says that it's not necessarily a huge deal.
For reference, I always use Mobil Clean 5000 (10W-40). I change my oil every 2500 - 3000 miles. My car has 146,000 miles on it and the car burns absolutely no oil, but then again, that could be an M42 thing.
Edit: Can I ask why you changed to Bosch +4 plugs?