I personally would go the headers then later add the edit, that's what I'm going to do
If you could or are only to get one, I would get the edit, my reasons for saying that are if you got the edit with a custom tune now, then got the extractors later you may need to retune.
Looking at what simon is getting from his edits, i really don't think there is much choice, Go the edit from Xtreme
There is no substitute for cubic inches but my pursuit sure closes the gap
*UPDATE * Pursuit has just run 11.763 and 116.18 mph making it Australias Quickest and fastest unopened boss as well as Australias Quickest and fastest naturally aspirated Boss