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' | 1M N54 Swap | Gruppe M CF CAI | VRSF FMIC & DPs | ER CP & Dual Oil Coolers | Dual 2.5" Piping w/X-Pipe | M3 Rear Exhaust | 20" 310M | Michelin PSS 265/295 | F10 M5 & F30 ///M Brakes | KW Variant 2 | H&R Sways | BMW Performance Grills w/Tri-Color | Custom ///M Body Treatment w/CF Splitters & Diffuser | CF Trim | BMW Performance Shift & Handbrake Knobs | BMW Performance SS Pedals | M3 Dead Pedal | V1 Hardwired | Int LEDs | Umnitza ICE VXX AE & More