Compressing my collection of anime
Re-encoding will introduce generation loss and encoder specific artefacts. Of course you are not going to encode a file 100 times and you are trying to preserve as much quality as possible, but with such vage ctriteria as encoding 1 TB of unkown quality, noise, bitrate, picture size, framerate and so forth there is much that can go wrong. Best advice: don't re-encode at all, particularly if you are not encoding from sources e.g. disks but web formats or already re-encoded content. Save the money spent on energy to buy more hard drives and learn to manage them (hint: ZFS). If you cant wait for encoder improvements and the next generation of super high efficient video encoders, then H.265 one of the better solutions currently available, but you'd have to take a close look at each file and how it was encoded, if you find that a video was already encoded on an i7 equal or better than yours with H.264 and that already took a day or more than you know you are going to spen 2 to 4 times as much. And you'd still have a bit of generation loss even if you got everything right. Also don't expect that software always returns perfect results, you should check every re-encoded file to be sure. And you shouldn't overclock your hardware or swap version numbers of software components used.

Buy a bigger drive if you don't want to go down this route, you save valuable lifetime and electricity.