Thanks for the welcome Oak & Rick! Most of you know more about Oakleys than I do, but I'll try my best to leave something where it could be useful.
Lenses cut from any 8.75 base curve (curvature in the front surface of the lens), which most Oakley lenses are, would be no different optically than original Juliet lenses, unless, of course, the cut is bad and severe internal stresses are introduced when mounted on the frame. This is still not much different than original Juliet lenses, since most Oakley and CNC cut lenses are identical, but it's the x-metal frames that have variations.
Lenses cut from M Frame lenses, Wrap 6.0 & Rake 4.0, are a different story. These actually have to be bent slightly to insert into a Juliet, Penny, & X-met XX, so theoretically there would be an optical distortion. In reality, it depends on the wearer. I wore +Red mounted in an X-metal Penny today, and I could not notice any distortion or experience any long term effects. However, I have had a customer who ordered +Red Juliet lens (now discontinued) that complained of some type of distortion.
Whenever lens is mounted in a metal frame, there is usually some internal stress that may cause visual distortion. One way to see the internal stress is to wear polarized sunglasses and hold a test sunglasses between you and an LCD monitor. You should see a stress pattern in your lenses, but unless it's really severe, it's usually harmless.
Image is internal stress pattern on a stock Oakley Big Square Wire Chrome Titanium Clear sunglasses.