I dropped 2 lbs per corner by switching from PSS's to Conti DWs a few months ago. I had no idea they were lighter, but the difference was felt IMMEDIATELY, so much so that I went straight home and Googled the weight of both tries, and sure enough, 2 lbs less. That's not insignificant!
Years ago I put 12.8 lb forged BBS RG-F's on my Scirocco, replacing older BBS wheels that were around 19 lbs. Talk about a MAJOR transformation! Losing unsprung weight really is a big deal. It's a cryin' shame that the 135's are so heavy, given that they are a great-looking wheel and unique to the ZHP (here in the US at least).
'21 M2 Competition
'08 Z4 M Coupé
'19 Golf R