There are 3 TSW RotoForged wheel styles that are available currently.
The lightest are the Interlagos, the other 2 are Nurburgring & Panorama (new) You can check these all out on TSW website, looks, sizes, weights etc.
Mine came from Discount Tire... Were $256 ea. plus they gave me a $100. discount for their sponsorship at G8 Natl Meet. Also heat treated my Nitto DR's. Michelins 235-50-18" came from TireRack.
Have dealt with them since 1987...
In 20" size the 8.5" 40 offset wheels weigh from 22 1/4 lb to slightly over 23 lbs.
In 20" x10" 40 offset they weigh about 24 1/2 lbs.
Next you need to fit tires, which start at around 28 lbs up to 35 lbs. So... you get lots of visual fluff, but not more than around 10 lbs a wheel/tire savings. Stilll... 40 lbs is 40 lbs!!!!
When I was running 285-40-18" Nitto DR's on the front, those tires weighed 30 lbs each vs. my 17" 175-40-17" Hoosiers for my G8, that only weigh 22 lbs.
Another thought is that smaller diameter tires mean that the weight is closer to the hub, which also helps performance. And, with my H & R springs, the actual space between the top of my fender well and tire is about the same as stock. Overall, my Flex is 3" lower than stock.