Damn, wish you had found some of my ads sooner. Oh well, yea, you can turn the E83 into an awesome handling machine. It's still 4000lbs, but that's only a couple hundred pounds (or a little more) heavier than a fully loaded E90.
If you have the chance, check out which suspension bushings from the E46 M3 fit the X3 and enjoy, they are a definite improvement.
Prototype 2007 Monaco E83 'X3M' | N54 Swap | Gruppe M CF CAI | VRSF CP & DPs | CXR Intercooler | ER Dual Oil Coolers | Dual 2.5" w/X-Pipe | M3 Rear Exhaust | 20" BC Forged HB05 | Michelin PSS 265 & 305 | F10 M5 & F80 M3 Brakes | KW Variant 2 | H&R Swaybars | TMS Z4M Camber Arms | Z4 Finned Diff | BMW Perf. Grills w/Tri-Color | Custom M Body Treatment | CF Trim | M Perf. Carbon Shift & Handbrake Knobs | BMW Perf. SS Pedals | M3 Dead Pedal | V1 Hardwired | Int LEDs | Umnitza Orion v4 AE & More