what would be better a single 5830 or dual 5770s
Dual 5770s will give better performance.
Dual 5770 will be much faster. A 5830 is only little faster than a 5770.
Dual 5770 will be equal to 5870 .
I personally feel that for a little bit more the HD 5870 might be a better choice than 2x HD 5770
but for me money is a very big issue i cant go over my spcific limit