I can't answer your question on weight. In terms of perfornace, the package shaves about a 1/2 second off the 0-60 and 1/4 mile times - this according to magazine tests.....
Performance Package (ZHP) -
Engine mods (new camshafts, re-programmed ECU, & lighter flywheel) for 10HP & 8 ft/lb of torque
Redline increased to 6800 (from 6500).
6 speed short throw shifter (auto available starting in '04, and no SMG with ZHP)
3.07:1 final drive ratio (instead of 2.91:1)
Max speed limiter set to 155 mph (instead of 128)
New M suspension, more "sporty" than standard sport package:
Firmer springs (front +6%, rear +8%)
Firmer shocks (Jounce: front +50%, rear +20%), (Rebound: front +35%, rear -8%)
Larger diameter anti-roll bars: 23.5 mm front (v. 23.0), 18.5 mm rear (v. 18.0)
More rigid forward bushings
Lower ride height by 15 mm (.6 inches) utilizing shorter auxiliary springs
-.5 degrees of camber
BMW M exterior trim elements - front & rear fascia, side sills, & trunk lid spoiler (front and rear fascia, & sidesills often referred to as M tech II body kit)
Unique exterior trim: anthracite (charcoal) headlight & foglight surrounds, high-gloss shadowline (black gloss) trim around windows
Large diameter stainless steel dual exhaust outlets
Extra thick Alcantra steering wheel
Sport Seats - Alcantra & Cloth upholstry to replace leatherette and standard trim (leather still an option)
Choice of "Black Cube" or "Silver Cube" trim (trim is across dash, around shifter)
Red needles on the instrument cluster
Unique 18" Wheels (style 135M), 18x8.0" front, 18x8.5" rear
Wider Tires: 225/40ZR-18 in front and 255/35ZR-18 in the rear.
Article from Car and Driver - http://www.caranddriver.com/article.asp?se...8&page_number=1