[KingLT1]

I would install a CAI and Flex fuel sensor, purchase HPtuners, and get a remote tune. Make more power with this for a fraction of the cost. E60 alone gonna be a 40-50whp gain. Probably gain 60-70whp with these 2 mods. Next mod for me would be a ported Supercharger and TB.

Headers would be last unless you install them yourself or find a shop that will do catless simply because a lot of places won't do catless headers anymore and the base cats that come with header kits are shit compared to stock. Only the GESI gen 2 hold up but they are expensive.