Just want everyones input on this, I think it obviously depends on how you use your system or what you use it for, but I think the 3800 is a better choice right now:
X2 3800:
http://www.newegg.com/Product/Product.asp?Item=N82E16819103562
4000 San Diego:
http://www.newegg.com/Product/Product.asp?Item=N82E16819103529
X2 3800:
http://www.newegg.com/Product/Product.asp?Item=N82E16819103562
4000 San Diego:
http://www.newegg.com/Product/Product.asp?Item=N82E16819103529