I would probably go for the engine upgrade 1st. I have an '02 3.0i and I just recently did the DINAN engine software and transmission software install and I am EXTREMELY happy with the result.........it now has that extra punch!
I also put the OEM chrome exhaust tips on mine and I like that look too.......
Let us know what you do 1st.........(engine, engine, engine)
300 hp would be awesome in that thing...........what do they do?

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Sold - 2002 X5 3.0i - Steel Gray Metallic/Gray Interior
Mods: DINAN Stage 1 Engine Software; DINAN Stage 1 Transmission Software/OEM 87's!! /OEM Titanium Grill /OEM Chrome Exhaust Tips/OEM White Sidemarkers/OEM White Tail Lights/OEM White 3rd Brake Light/OEM Rubber Floor Mats/OEM Titanium Liftgate Handle/'06 Sport Steering Wheel

2005 Mercedes Benz ML350 Special Edition
2007 Mercedes Benz C230 Sport (for work)
1989 Ford Mustang GT (all original w/80k miles) my TOY!