change to 1.67 or thinner lens ofcos will have difference lar, becos higher index means thimmer lens, so in turn lighter in weight. Different brands actually i dont think will have much difference, most most important is the SIZE of your frame. Like me made a linkskin frame few mths ago, very lightweight cos i select a mre elongated shape so not that big in size so thinner lens less weight. Then i made an IC!Berlin last week and i selected a mre squarisn & bigger rame size, in the end oh my gosh, the lens thicker & heavier. I mean IC!Berlin frame is very light, so by comparison of both specs, the problem could not be the frame, so it has to the lens. And both are compared using same type of material & index, which is HOYA 1.67 double AS plastic lens. So as you can see, it is very clear that the frame size plays a very big part in determining the overall weight of your specs. Please dont make same mistake as me again!