basicly its okay.
but hardly 58x0 is max "cost/effective", cuz 69x0 already cost as much[you can get 6950 for ~$250 today] and do more MH/s, but they more "power/effective", a bit. actually its more noticeable in BitCoin-unrelated GPGPU workload, like [Huge-HR/DR]image-processing or AV/match crunching.
[virtually]any GPU's brands is okay, but reference GPU design boards/cards/coolers is better[overall. without compromising one or another aspect of design/usage. which is usual for "alternative design" boards], while being little noisier.