So i upgarded to the One X right when it came out and received no actual performance increases other than graphic and frame rate increases. If those are your issues then just the Xbox will be good for you. If you want decreased load times then you need a SSD.

I used to have terrible loading issues. It would talk me abut 90-120 seconds to load in to crowded cities and sometimes I would load in to the city, walk 10 feet and get another 30 second loadscreen. Ever since putting ESO on an SSD my load screens are basically never more than 20 seconds even at extremely crowded wayshrines. Also I used to have a problem with having to wait for NPCs and crafting stations to load as I walked up to them. Sometimes I would have to wait up to 30 seconds for NPCs to appear especially at the undaunted camp. Since I put ESO on an SSD i no longer have to wait for any of this. So if your goal is to reduce load times then I highly reccomend buying an SSD. You don't even need a One X to see these load time decreases as I've tried it on my original Xbox One too.

As far as crashes go, I still experience about the same number of crashes as when I was on a normal Xbox with no SSD. In DLC areas and frequently in Cyrodiil my Xbox will make the stuttering noise and instantly crash to the dashboard. After discussions with Xbox support these kind of crashes are coding errors and no amount of money we spend on our end will stop those if that is what you are hoping to solve with an SSD and new xbox.