If we put aside all the driver issues that have been highlighted in the past few weeks and look at the FX series in comparison to the GF4 series, then the whole range is shaping up quite nicely now. The only blip so far has been the NV30 which was crippled by being restricted to a 128bit memory bus.
The NV34 based cards (5200) have a performance that is roughly on par with the GF4MX but excels it when FSAA and\or AF is applied. The best thing is that they are bringing DX9 straight into the mainstream market which is something that ATI haven't managed to do yet. Passively cooled or with a standard fan, these are almost silent.
The NV31 based cards (5600) are sometimes outperformed by the Ti4200, though that is usually in multi-tetxturing situations where the extra TMU per pipe in the Ti allows it to gain ground. Again, as soon as you include FSAA and AF in the equation, the FX moves well ahead. The change from wirebond packaging to flipchip has allowed nvidia to crank up the clock speed, from 350MHz to 400MHz, and this has had quite a large affect on the performance. I would think that there should be some overclocking potential in this chip. The chips can throttle themselves depending on hwo much stress they are under, and can go from silent running to average card fan nopise levels.
The NV35 based cards (5900) are, I'm happy to say, real beauties. They perform very well and have lots of headroom to use high levels of FSAA and AF. At resolutions above 1024x768 with full FSAA and AF they are head and shoulders above their bretheren (and the competition
). It's a shame that nvidia didn't allow this chip to stand up for itself and resorted to driver *cough* optimisations to try and make it shine. The cooling solution is slightly! larger and you lose a PCI slot. But it is pretty quiet and can even become silent if the card isn't doing much. I think the various board makers are coming up with cooling solutions of their own which may take it back to a single slot solution again.
There will probably be a NV36 sometime in the future to replace the NV31 or maybe slip in a market between the Ultra high end and the Ultra mainstream.
As CC said, FSAA on the Radeon series is by far the best. But the FX series have a slightly superior AF algorithm. In comparison the 9800Pro has the edge over the 5900Ultra in image quality and speed at lower resolutions but move beyond 1024x768 and the 5900 pulls ahead due to it's higher memory bandwidth. At 1600x1200 with 4xS FSAA and 8xAF it's quite a thing to see running. The 9600 and 5600 were quite evenly matched but the move to the flipchip design by nvidia has given them a distinct clock advanatge and the lead. I expect ATI board makers will respond by releasing overclocked versions of the 9600 though, so it might be a very even match.
Roll on Christmas and the NV40 Vs Loci battle, that's the one I want to see. All the technologies out there at the moment are test beds for the real contenders and I think they have been released to mainly recoup R&D dollars for the reall battle