I know this sounds crazy, but are you sure the fans are blowing in the right direction? I read a post here last month where the guy was having major cooling problems at idle and couldn't figure out what was causing it as the rad was good, the water pump and thermostat were good, and the aux fans came on right when they were supposed to. It turns out that the fans were spinning in the wrong direction so instead of pulling air from outside the car through the radiator to cool it, they were pulling hot air from the engine compartment through the radiator which wasn't helping the temperature.

If I remember right, this happened because the aux fans had been plugged in backwards when they were removed at some point. Do a search, I'm sure you'll find the thread. If you want to check yourself, take a piece of paper and hold it up in front of your grille when the fans are on. The paper should be pulled towards the grille. If the paper is pushed away, then your fans are turning in the wrong direction.

Its a cheap and easy thing to check, so as crazy as it sounds, give it a look.

Jonathan