Get the card now. It's a great performer at a great price. PLUS, DX10 cards will be expensive when they come out for awhile. PLUS, very very few DX10 games for awhile. PLUS, give manufacturers a chance to work out the bugs on the DX10 cards (don't be their guinea pig). PLUS, if you wait you can see what the power requirements will be and whether or not you need to upgrade your PSU. PLUS, you can enjoy your gaming NOW instead of waiting at least half a year.....life's too short, enjoy it now.
When you look at it those ways, seems like a pretty clear choice to me