As for the case, cool build ! but I don't plan on going up to the scale of replacing the GPU cooler / messing with the case fans (unless I will be ultra annoyed by the end result). But it seems that in your case (playing non demanding games) the temp of the GPU is a non-issue.
There are a lot of quiet GTX780s, like the MSI GTX780 gaming, but there are others that are noisy, personally i never tried the evga acx... but from what i read was not that quiet. I didnt need an aftermarket cooler for it, was just more a hobby/project for me, simply got tired of wating for the custom coolers, and took a reference one with the intention of testing aftermarket. About the fans, the included are decent fans, not bad not great, but i would suggest to get one more though, as the R4 only comes with 2, Antec True Quiet 140
are very cheap fans that are very good for building a quiet R4.