Yup, as long as it is the same model - e.g GTX480, it will work fine. Obviously, it would be advised to get the same brand if possible but worst case scenario you end up with one Gigabyte and one ASUS (as an example) it won't cause any problems.
Hello and yes thats true. As long as the GPU model is the same you are good to go. Doesnt matter if its palit + evga, an overclocked card + a stock one or even a 1GB + a 2GB card. They will sort it out between them as long as the GPU is the same.