To be honest, depends on your patience and budget.
You've made it this far, I would say best to wait end of Janruary...
Why? The 580 will be launched including the G71, which in turn will
give you a fresh product cycle to choose from, not to mention drive down
the price of the GTX should you choose to stick with it.
I dont think the X1900 is going to be 48PP bud.