XFX is just a company that makes video cards based on nVidia's graphics chips. XFX just uses nVidia's GPUs, solders them to a board designed and manufactured by themselves, and sells it. eVGA, MSI, BFG, these are all companies that make video cards. nVidia does not make any of their own cards for retail.
XFX often produces overclocked cards that run faster than stock variants and sells them for a price premium. If you only paid $25 extra, it's probably not a bad purchase. Just depends on how much it's overclocked versus how stable it is versus how much the stock version would cost.