I have no idea what funds you have but i build pc's for a living. Depending on what game you will play, i would build a streaming box that can do both encodes so that you can switch if a game is better on one encoder and not the other. Typical scenario is PUBG, BLOPS, Apex who all look quite a bit better (in my eyes) on x264.
A ryzen 5 2600, 16GB PC3200 ram and a GTX 1660, 450w decent powersupply. With that cpu, you can stream at medium x264 settings and with that gpu, you can stream at max quality. I have had great success with NDI Scan converter so that i can play my games at maximum settings with a lagfree stream. Usually, with OBS on both machines, OBS on the gamer takes up so much gpu resources. With the scan converter, that isn't the case.Agood capturecard will probably always be the best though. Especially if you want to stream Vulcan games. Rage 2, Wolfenstein etc.
Word of advice though: If this is for Twitch (since you mention stream), a 720p max quality stream will almost always look better than a 1080p due to the bitrate restrictions of Twitch. But for youtube, this changes a bit. Not sure what the restriction is on YT now, but last stream i had was 18mbit 1440p that worked flawless.
Sorry for the long post, but this is my 2 cents.