Yeah, I expect the S4 will have a 5" 1080p screen (or similar) because it seems like everyone's flagship will next year. Does that matter to you compared with 4.7-4.8" 720p?
But there is not a word of certain fact about its specs or release date right now. Everything you read (including what I wrote above) is rumour and guesswork, with most rumours starting as someone's guesswork.
I'd say it really comes down to whether you want to buy now, with the current phones well established, or be an early adopter of one of next year's in (probably) a few month's time?
One X+ vs S3? Have a play, see which you like best. They are both good.