Just to pop a quick note in here ... the Radeon9700 is just released, and is priced at the same price point as the Parhelia512 but offers more than double the perf. I know you said perf aside, but that is a huge diff! The Rad9700 also does 10/10/10 RGB which is precisely all the Matrox marketing blurb of 'Gigacolor' is. However the Rad9700 is also fully DX9 compliant and as such uses FP precision throughout AND is also capable of 128bit colour, both of which should enhance IQ considerably. 128bit colour is certainly FAR superior to 10bit RGB/Gigacolor and is applicable to games as well as just apps, unlike 10bit RGB/Gigacolor. Of course the Rad9700 has yet to undergo rigorous independent testing and is about a month away, still worth noting though. In any case I wouldn't expect the IQ to be right up there with Matrox Parhelia, but certainly very close behind.
So is the Parhelia worth the extra cash? IMHO it depends upon what resolutions you run in, if you want better than GF3 3D perf, can utilise 3 monitors and the quality of your monitor, LCD would seem pretty pointless, as IQ optimisation is really key in all of the DAC of CRT technology, but esp for 10bit RGB. You'd certainly get a lot more for your $400 with the Rad9700. But in a few months there should be a budget Rad9700, the Rad9500, if not a budget Parhelia512 (256?), and all cards should fall in price anyway with the increased competition esp from the up-coming nVidia newby due November.