BBS wheels are very nice. If you like their style. They are also very strong and very light.
As for light wheels.
They should MAKE a huge difference.
You cant do tests with two different cars. It just wont work.
On my first lexus. I had some heavy ass 19" chrome AXIS wheels put on it. Riding with those and then going back to the 16" winter wheels. The car was night and day. Acceleration was tremendously different and braking too.
Saving any UNSPRUNG weight is Very benificial