Normally, I don't go for the high end rigs. I use Linux so it makes sense to use hardware one or two generations back so that I can be sure of good hardware support.

But basically for me, choose a motherboard and upgrade until I cannot upgrade anymore. i.e socket change or capacitor ageing killing the motherboard. New graphics card as long as it fits and I feel there is going to be a performance increase.

For me, continuous, incremental upgrades are more practical than buying everything at once.