Ar design have some nice fitting DP's mate, thats a good option. As above BMS DCI, and if you want to get a FMIC to increase efficeny then do that.
ETS make a reasonably good one, AA has one, pretty much everyone lol.
I would go in order of
tune
FBO - dci, downpipes, fmic etc
meth
then get nasty and get RB's
