I just got done dusting off and upgrading mine. Went with G.SKILL Ripjaws 16GB DDR3L 1600 CL9, a leftover Toshiba SSD, and an i7 4790S I pulled out of an old Optiplex. At some point in the past it ended up getting an Intel 7260 wifi chip so that's fine. About the only thing left to do is put an Xbox One Wireless Controller receiver in it, but I really don't know what I'm going to use this for lol.

As for overclocking the GPU you should be able to max out the core clock to +132 and the memory should be able to do about +700~800. The 4790S under full load tops out at 2.9GHZ, I'd imagine the 4770S will be about the same.