Finally sussed out how to get the Gfx running topped out using HiResTexturePack without any glitching.

Disabling VSync is a given, as is not using FXAA.
Anyhoo, use the launcher to set everything to Ultra,
completely disable AA and AF and then just use your GFX Card panel to set them to 8x and 16x instead.

I cranked Tessellation up to 64 and other stuff in the Catalyst Control Panel right up to see how they performed, and there was nowhere near the performance hit as using the Game settings for AA and AF.
Even using Super-Sample AA mode runs fine.
(Tbh Tessellation beyond 16x isn't really needed)