Yeah, the latest polycarbonate lenses are really thinner than high index plastic lenses like 1.67 index lenses. If you have the high prescription in the eyes, you'd better choose the 1.67 index polycarbonate lenses which will not let you look nerd. This material of lenses will provide the perfect eyeglasses for you.
Though polycarbonate lenses are thinner than common plastic lenses. But that not means polycarbonate lenses are thinner than all types of plastic lenses. If really have very high prescription, you can try to buy 1.74 index lenses. As far as i could know. 1.74 index lenses is the thinnest lenses for people with very high prescription lenses. You can have try.
Yes, you should know that polycarbonate lenses are known to be safer and thinner. And also, they are also known to be thinner and lighter than traditional type lenses, such as the plastic lenses. And also, Polycarbonate lenses offers you total protection from UV light and radiations. But ordinary plastic offers you minimum protection from UV light. And there are also many other advantages of polycarbonate lenses. For example, they are convenient to be used. And, If you use plastic lenses, you may need to invest in antiglare material to protect you from any harmful rays. So in my opinion, you should choose Polycarbonate lenses.