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 E83 2007 Monaco 'X3M' | N54T Swap | Gruppe M CF CAI | VRSF CP & DPs | ER Dual Oil Coolers | Dual 2.5" Piping w/X-Pipe | E92 M3 Rear Exhaust | 20" 310M | Michelin PSS 275/305 | F10 M5 & F30 ///M Brakes | KW Variant 2 | H&R Sways | BMW Performance Grills w/Tri-Color | Custom BMW ///M Body Treatment | CF Trim | BMW Performance Shift & Handbrake Knobs | BMW Performance SS Pedals | M3 Dead Pedal | V1 Hardwired | Int LEDs | Umnitza Orion v4 AE & More