D3 is a very fast, moderately stable driver with a unique flight path. It is designed for all players and flies extremely far. What separates the D3 is its ability to flip up and then glide without the extreme drift to the right or the hard finish back to the left.
The 400G series is the regular 400 plastic with a shot of adrenaline. It is the base 400 plastic mixed with another resin that give the plastic a slightly different feel than the base 400 series. The additive also makes the disc more durable and requires more time to break it in.