If you are going to use double layer dvds, make sure to only use Verbatim brand. Though if you are in the US, Falcon brand DL dvds found online are a reasonably good substitute, they are just not found at local stores.
Personally, I never burn DL dvds at their highest rated speed when burning on computer drives. With your Pioneer recorder, I'd take it down a notch also. You only save a small amount of time and introduce a bit more uncertainty to the quality of your burns by burning at max speed.