Hard to say. For some activities, the iPhone X battery is WORSE than the plus. Compare the X to the 7/8 on Apple's site. The X has the same web browsing time (12 hours) as the non-plus models! In some other areas (i.e. talk time), the X is equal to the plus.
Problem is, more people use their phones for web browsing (or the equivalent using various apps) than they do for talking these days. So for some, the X may not yield ANY improvement over the non-plus iP7/iP8 and will be a step backwards for plus users if Apple's specs are accurate. Sad.