Sometimes it makes me wonder if Im the only guy around here who is unable to swap computers ever 2 months like if they were a pair of shoes... humm... I guess that makes me special.
Since money doesnt seem to be a problem, I'd go for your second choice ("spare" computer).
Maybe in the 2008, you will see a clear panorama with a couple or more DX10 games in the market.
So it will make the videocard decision a bit easier IMHO.
Maybe I dunno, we'll be able to see the new G90 cards from nvidia as well.
Then also we'll have penryn, so you either buy that, or a really cheap by then quad core.
Or maybe we'll see what's the deal with the phenoms.
So it just seems to me you might want to have the best of the best, so better wait at least till things with DX10 are clear and make your choice.
And if you're not happy with it, then you can wait for R700 or maybe even Nehalem.