let us not forget, video cards have absolutely NOTHING to do with rendering performance.
Perhaps you are wanting faster real-time preview (which is not real-time rendering, no matter what anyone else says).
I am in the same boat looking for a good compromise between what I can afford and what workstation graphics are available.
Maybe LW8 will support Direct X 9, but probably not. If you have apps that require DX9, then get yourself a card that supports it, since DX9 has some real nice real-time shading characteristics. Otherwise, get an older workstation card like a wildcat or fire gl. They may not support directx, but when you’re using LW it don’t matter. The older fire gl cards supported direct x 8.1.
If you’re wanting raw rendering speed increases, get a computer with a fast front-side bus and tonnes of ram and dual-processors. AMD is a great value for money right now.