A fuller explanation
I appreciate that my comment about the 2600 XT being a disappointment sounds a bit contradictory but I stand by it, and here's why.
AMD has known the specification and performance of the 8600GT and GTS for ages and it could choose to put as many or as few stream processors into the 2600 chip as it liked, and of course it could set the price at any point that it chose too.
The performance and pricing of the 2600 XT is, therefore, a carefully considered decision that AMD should aim to beat the number two chip (the 8600 GT) by a tiny margin.
That's probably a sane, practical and wise prove but nonetheless it disappoints me.