I don't normally go underneath 10000 wt diff oil with a one-way equiped car. I ran 20000 wt normally but am going back to 30000 when I decide to race touring again. A lighter diff oil will take away onpower steering while giving more stability in low traction conditions (I also believe it will give you more offpower steering as well, which really isn't needed with a front one-way).
You might want to turn the amount of steering throw down on your transmitter. It should be set (either by subtrim or by steering dual rate) to allow you to go around the narrowest turn on the track but not much more. This will do two things for you. 1. It won't allow your rear end to swing on you because the front end is turning just as hard. 2. More importantly, it will give more cornering speed by not allowing your tires to scrub speed away from the car.
The Helios Advanced High speed is meant to be used with 2 digital servos, the Super High speed you can use 1 digital and 1 good analog, Normal is for everything else. That being said, I was using the Advanced setting with a digital servo (Futaba 9451) for steering and an analog (Futaba 3010) fior throttle. If you use the Advanced setting like this, watch your analog servo closely (watch for heat and any other weird behavior).