I posted this in the wheel forum, but am putting it in here too since this thread helped me with figuring out what new wheels to get. The new wheels I got were 17" Assetto Garas, which replaced my 18" THP wheels.
I was figuring to lose about 10 lbs per corner but ended up with just 6 as the 18"ers weighed 46 lbs and the Sparcos (with ContiProContact 215/50 LRR tires) 40 lbs.
However after a couple thousand miles, I'm seeing about a 10% increase in mileage (3-4 MPG). When summer comes around, it'll probably be even better