A GF FX from what I have read up about it (I'm buying a new system soon) is gonna wipe the floor with just about everything out there in gaming terms. And I'm pretty sure that the card will handle maya very capably. However I'm not sure what the price will be but I'm sure it will be upwards of £300 (GBP) and for that price you could upgrade a CPU and buy a GF4. As BabyDuck has said there are not really any CPUs that can push a high end graphics card.

So my main point is that can you justify to yourself and your wallet the cost of a GF FX and as was already mentioned it'll be outdated in 6months.

I would buy the highest spec GF4 / Radeon that you can afford and use what's left to upgrade other components.

To answer your question 8x agp shouldn't ever be a disadvantage in the near future unless it raises compatibility issues with your other hardware. But if that's the case it is backwards compatible so you can knock it down to 4x.
Sorry to ramble!
Alan