I'm thinking about buying another 1TB hard drive.
I might want SSD's but not for now.
I'm thinking about SLing my GTX 580 but apparently the Sabertooth P67 doesn't do well for SLi/Crossfiring
I would say your build is good but there may be unnecessasry spending. The i5-2500k is good enough for you. I don't think you need the hyper-threading. Either way you have it now haha. You will be fine doing sli with the Asus Sabertooth, it will be at dual x8. If you're buying another HDD please go for the samsung spinpoint f3 for $60. It's recommended by all of us. It has like the best performance among 1TB HDD. It's only $60: http://www.newegg.com/Product/Product.aspx?Item=N82E16822152185