The x1900 CF card is clocked exactly like the 1900xt, so unless you are planning on going for CF, you may want to rethink. My 1900xt is plenty for me at this time. I built my new rig in April, and I'm not going to get Vista for a good long while; so the trick is what is a cheaper upgrade when I need one?
If I can find a 1900CF edition for under $300 later, or spend @ $160 on Vista upgrade plus $400 on a DX10 card. Choice 3 is to live with it, and drink more beer. No choice at all, really.