About your fans...on my E320 I thought they might not be working as the temp reached 110C on a hot day with the a/c on...but they were just running at the slow speed. I think they should be running maximum by 115. I know the 300 is a different motor, but on my car fan speed is first tripped by water temperature. There is a single wire lead off the Water Pump, this is for the dash guage...then there is a four wire clip which goes into the harness. It might be brittle...be careful...but with the engine running just pull off the clip and the fans should operate at maximum. Maybe it is different on your car, or maybe this is the problem.
As a last resort to combat overheating, you could always wire the fans directly to 12V with a dash switch inside the car (even in one of the extra slots in the row of toggle switches) and just flip the switch when the temp goes up.

__________________
________________________
2002 Mercedes-Benz E320 4Matic
1995 Mercedes-Benz E320 Wagon
2005 Land Rover LR3 V8 SE
1999 Audi A8 4.2L quattro