I have a -8 and -7.75, so I know your pain.
I have high index polycarbonate lenses, and I would highly recommend them, especially if you want to use frames that will use big lenses. With a low index lens, it needs to be thicker to refract light at the necessary angle to correct your vision. With a thick enough lens, you get weird distortions near the edges of the lens (where it will be thickest). I've noticed this in my sports goggles, which have the same index as my normal glasses, but have physically bigger lenses. I get a weird vertigo feeling whenever I put them on (thankfully, it's pretty mild, and I don't wear my sports goggles often).