congrats on the purchase! mods i've done so far on our X5, mostly comestic:

-titanium grilles (prefer this over gloss black OEM performance)
-oval exhaust
-OEM aero kits
-updated LCI taillights
-///M footrest
-rear shades

did you get petrol or diesel? you'll get noticable gain if you install a diesel box (DTUK)or a tune (bluefin) on the X5.

for twin-turbo petrol, procede or JB4 would be the good.

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'07 X5 3.0d - Black Sapphire Metallic / Camel interior
Specs: Sport pack, Executive, 7 Seats, OEM 336, Hifi
Mods: Aero Kits, Titanium grilles, 4.8i exhaust, Tinted, ///M Footrest, OEM Sport pedals, OEM Rubber mats, OEM Sunshades, LCI Taillights