I am getting some 3 year old lenses replaced and have the choice of paying in the region of $150 for CR-39 1.74 index lenses from selectspecs.com or around three times as much for my local optician to put in Essilor's 1.74 index lenses. Selectspecs says they manufacture their own lenses, and that they have an Abbe value of 33 and specific gravity of 1.46. With a prescription of -9.25, do you think that there will be any visible difference in the thickness the lenses? Is there any other difference that I should be aware of...?

Many thanks for any help you can give.