Q: How does a Lexan swap compare to lighter wheels for saving weight?

They target different weight. Lighter forged wheels remove unsprung, rotating mass, which sharpens acceleration and braking as well as ride quality. Lexan windows remove body weight up high, lowering the center of gravity, and can strip about 23.5lbs. Serious builders often do both, and pair them with aero such as the Ascension-RR rear carbon fiber wing; if you already run light wheels and want the next weight reduction for a race car, the windows attack mass that wheels cannot touch.