The greenstuff is much better for track work apparantly.
Can't remember off the top of my head how much the RB74's are, but they aren't as expensive as Greenstuff iirc.
Both types should be piss easy to chase up
RB74's rock,
When I upgraded my brakes to slotted rotors, we used these pads and I am very happy with their performance, the only negative I have is the amount of dust they create with slotted rotors.