well, the best i can do is predict, but...the i7 920 was out on the market for a very long time, and i dont think they really even ever dropped prices, why? cause it didnt have any competition, and intel is greedy. intel is still greedy, and that cpu doesnt even have anything close to competition, so i doubt the price will drop much. if anything, it might take until next year when amd releases the bulldozer for intel to really do anything about its prices. so my prediction is 1599 give or take when the bulldozer comes out in 2011, sometime around Q4 2010, or Q1 2011...theres my 2 cents though.
i7 920 may not have dropped down in price but the i7 930 and the X6 is just about $15-$20 more. Some people will take that rather than the i7 920.
As for the Xeon X5680, it is already out at $1750: http://www.newegg.com/Product/Product.aspx?item=N82E168...
pretty steep price but I guess for enterprises running mission critical application it will be worth it. But I doubt it will go down in price. It may soon be replaced by more powerful processors and retired rather than lowered in price.