I've been mining for a few months now. I have 6 AMD 7950's that average between 500-550 Mh/s. From the bitcoin hardware mining comparison you can get a glimpse of the graphics card that would best suit your need for a rig. I don't believe servers would be a good mining choice since they usually don't have graphics cards in them. So my 2 cents would be look over the chart here: https://en.bitcoin.it/wiki/Mining_hardware_comparison and make a decision off that. With my 6 cards I currently mine at 3.1 Gh/s and with the pool I'm in get between .09 and .12 bitcoins per day. Best of luck to you!