An i7 Haswell should have enough grunt ....
In case that leads you to think "Gosh, here's someone that can identify the generation of processor from the number" I use an i5 4690 Haswell, and I've recently looked at the cost benefit of swapping to an i7 compatible with my motherboard which would help run my VMs (answer: not enough)
All that translates into it being likely that you will be in a similar position, to upgrade will be a motherboard/processor swap at minimum. If you need the additional compression of the H.265, or you just fancy an upgrade, then it might be worthwhile, otherwise just convert to H.264 and you will have plenty enough power to do the editing.
Finally what are you using to play your video? Part of your issue may be Windows. Try VLC, it may be as simple as that.
ETA doh! grams =/= bobby, regardless of the similarity of the avatar.