well, i do have both cards, and i know their advantages and disadvantages, in both image quality and performance. i know how both run the farcry and ut demo, as well as daoc (which i am most familiar with, as it takes most of my gaming time), halo, call of duty, and bg1942 (desert combat).
there are some subtle performance differences in both performance and iq, however they are not all in ati's favor (but that's another discussion entirely). i overclock both cards, and my 5900 is FAR more overclockable than my 9800pro, which does indeed help make up for some of the 5900's defencencies.
as for your gf2/gf3 comaparison, that holds no relevance as they were different generations/architecure; not like the r3xx supports dx10 ;p
bottom line, and the point i've been arguing the entire time, is that while the ati is indeed the more capable part in dx9 (and nv has closed the gap somewhat, and may further with custom codepaths/optimizations), by the time dx9 titles form the majority of the market, neither card will be a very viable alternative. if the 9800xt, the fastest card available to us at this time, barely plays farcry at 40fps (and this is without aa/af remember), i just cannot see a vaild reason to think it will be viable in another 12-18 months when dx9 titles overtake dx7/8 titles. 2 years is LONG time for a gfx card these days, and the 9800p, while a great card, is already a year old.
in all the arguments you've made, i have seen nothing that would make me think otherwise, based on comparing both of these cards in everyday use. there is no reason for me to believe my 9800pro will stay in my pc any longer than my 5900. there is not "futureproof" when the industry is running 6-12 month product cycles, especially when applications requiring their hardware "features" are 1-2 years behind the hardware itself. put on your rose-colored glasses and believe your current generation is more "futureproof" than the next guys.. but you're simply kidding yourself.