THE FX 5900 HAS FOUR PIXEL PIPELINES.
It's more advanced in some ways (double stencil ops per clock), but it can't output more than four pixels per clock, no matter what. You're not "getting technical" when you claim the 5900's four pipes are "double-pumped to make it a 'virtual' 8 pipes," you're just making things up. A 5900 can never output more than four pixels per clock, while a 9800 can output eight by virtue of its eight pipelines.
Now, just because the 9800 has twice the physical pipelines as the 5900 doesn't mean it's automatically better. GPUs are too getting too complicated to break them down to mere "pipeline x texture" specs. One GPU may take less time for a specific calculation than another, making it inherently faster per clock. You need to check out knowledgable reviews with well-explained benchmarks to see and understand how each card's unique architecture plays each unique game.
Most people recommend the 9800 over the 5900 because it's generally faster with AA+AF, it has better-looking AA, and all signs point to it far outperforming the 5900 with lots of DX9 effects--so what's not to recommend for the same price? But they're both good cards, each with good and bad points. nV's drivers (better dual-mon controls, Linux and 64-bit support) and lower price (5900XT vs. 9800P) may still make the 5900 a more attractive proposition to you despite its slower AA+AF performance.