Hi Peter,
If you aren’t doing any kind of 3d at all then you’re not going to get any benefit of a quadro over a geforce – all of the quadro benefits are geared towards accelerating 3d displays for animation and industrial design programs such as 3ds max, maya, xsi and pro engineer. That even said, a regular geforce 6800 gt has fantastic performance under a lot of these programs and the jump in price between the two is quite severe. For 2d stuff you won’t even task a 6800 gt – I’d go for one of these as they take up less space than the ultras, use less power and are quieter to operate. I’d save your money and put it into faster processors or more memory which is far more beneficial for after effects. Please note that a 3d card will never do anything to accelerate after effects rendering – it’s only recently that a few 3d rendering engines have started taking advantage of the onboard gpu of the highend quadro cards so you aren’t going to be looking at that filtering into after effects soon.
Personally I’d not bother with the quadro as it won’t benefit you, I’d go for quicker processors that will accelerate after effects or possibly look into a second monitor to plug into the second output of the geforce card if you aren’t already running dual monitors – the extra desk space within after effects when you are using hundreds of layers in an after effects timeline will speed up your workflow.
Personally I’m working on high end 3d and compositing and I’d find it really hard to justify a quadro 3400 myself – the acceleration benefit just isn’t enough to justify such a huge hike in price.