Hi Brendan,
A beefy GFX card really won’t help you much in AE I’m afraid. Open GL previews are usually not to be trusted for accuracy either. I may be wrong, but AFAIK it is the procs & RAM (and fast RAID drives to a point) that gives you the previews, not the GFX card. If you are working with lots of 3D lights, etc then OpenGL may give you fast response with certain cards, but not for running streams of video.
I’m not sure what you plan to do in AE, but if it’s just running several streams at once (eg: Picture in Picture or similar) then use something like Premiere or Final Cut Pro and make sure you have fast striped drives and at least 4 procs for full 1080 HD. There are hardware accelerated products out there, most notably ‘Axio HD’ by Matrox which runs with Premiere – that will give you more RT HD streams than most other edit systems on the market, but it’s not cheap.
Those big Quadro cards are mainly useful for 3D apps and colour correction systems like Assimilate Scratch or similar, or as part of a Smoke/Flame system. After Effects really doesn’t take advantage of them at all.
Depends what you are wanting to do, as to what system/software you should be using?
Hope some of that helps.
*Production Studio Premium CS2 / *Combustion 3 / Mocha v1
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Win XP Pro SP2 / Intel P4 3GHz / 2GB RAM / GeForce FX5200 / DeckLink Pro / Roland DS-5 monitors / Sony BVM-20G1E / DVS SDI Clipstation / Wacom Intuos 3 A4 / 110GB boot/80GB media/600GB RAID-0