Stephen,
Think the down-pipe is the most restrictive in general although the up-pipe is a limiting factor on re-mapping as if the boost is too high and EGT's go up the cat melts and goes into your turbo....
I have the same plans as you, de-cat up-pipe, down-pipe, ported OE headers, already got a panel filter and that'll be me for a wee while.... then fuel pump and re-map.....