The i5 2500k doesn't suck at everything except gaming, if that is what you mean.
It is more like the 2500k is a couple % better for gaming and a couple % worse for everything else, and the 2700 is a couple % better for everything else and a couple % worse for gaming.
No motherboard you would ever want for this would be anywhere close to $700.
Just get something like this and you should be finehttp://www.newegg.com/Product/Product.aspx?Item=N82E16813131792
- Edit - What you really should be asking is what PSU you should use to power all this.