My research tell me that good graphics cards are becoming scarce..
personally I wouldn't invest in these full size cards..There are smaller single slot USB cards that can be daisy chained, so you can add more as your funds grow..
My trade is air conditioning, so I'm just gonna say this; as we all know, the biggest enemy of your system is "HEAT"!!
The second thing is the energy coefficient status of your system, which is also known as the energy spent compared to the work done (profits from the mining)..Then there is overhead expenditures..