5x vs 5 plus battery life? Any word on actual performance?

Well, according to Garmin's specs Garmin 5x+ has roughly 65 % bigger battery than 5+. You have 5x, not 5x+, but the difference is about the same. And your experiences seem to verify it. 

I switched from a F3 to a F5+ and I have to charge the F5+ approximately every 5 days and the F6 before every 7 days.. This is absolutely reasonable because the F3 did not have Maps and Music and it is much smaller. If you want really Long battery lives, consider an Instinct Solar.

Both the 5 and the 5+ came with 3 battery sizes.

You are comparing the large battery version of the 5 to the medium battery version of the 5+.

If you compared a 5X to a 5X+ (both large), or a 5 to a 5+ (both medium), or a 5S to a 5S+ (both small), the comparison would be more equal.

By the way, you are shortening the lifetime of a Li-Ion battery by discharging it all the way to 0 every time. This type of battery doesn't really like being charged fully or discharged fully.

This may not matter much in a watch, which will be technically obsolete before the battery dies, but it just makes me cringe when I see batteries treated this way on purpose.

Advice on this forum and others is that this watch needs to calibrate the battery and that you do this by taking it to zero. And for sure the second drain cycle was slower than the first. Especially the last 40%. 

But point taken and I’m not doing it anymore. 

Advice on this forum and others is that this watch needs to calibrate the battery and that you do this by taking it to zero.

Yes, that is something you are supposed to do once or twice. You said that you were planning on doing it repeatedly, and that was the reason for my warning.

So I get it that I shouldn’t let it get to zero. But how do I keep it from charging to 100. Just keep an eye on it and unplug it? Or does the battery have logic to prevent topping off?

does the battery have logic to prevent topping off?

yes

But how do I keep it from charging to 100. Just keep an eye on it and unplug it?

There is no other option. You can't set the watch to stop before 100.

But charging to 100 is not nearly as bad as discharging to 0, so don't worry too much about that part.

But how do I keep it from charging to 100. Just keep an eye on it and unplug it?

You could install the Battery Widget with Automatic Charge Detection widget. This does not actually stop the charging but does give an alert at a user defined level.