6 vs 6x (Sapphire) for my wrist and profile? How are your battery experiences so far?

37.5cm wrist is enormous, like an elephant trunk, I'm assuming you meant 17.5cm wrist?

My wrist is 16.5cm, and I've got the 6x. I upgraded to it from the Vivoactive 3 Music. Here are my thoughts:

The 6X has 2 advantages, and 2 disadvantages. It has more 50% more battery life, and 0.1" more screen diameter and pixels than the 6. But it has more size and weight.

Like you, I don't usually do activities that last more than a few hours - and I also carry a battery pack for my phone and other devices when I do activities that last several days. Still, I picked the 6x for the 2 advantages I listed above. The screen size is amazing, it might not sound like it's much bigger, but it displays SO much more information than the smaller screens do. Even when diplaying 8 fields at a time, they are all very big and legible, and the map can actually be used like a map. You can really see and read the topo maps like a normal handheld GPS. Secondly, the battery life is excessive. Yes, excessive! And I'll tell you why that's important for me.

I frequently go out for hikes or other activities without really planning in advance, and sometimes my watch only has a 30-40% charge when I do. But it doesn't matter. I can hike for 4 hours and the battery only drops 5-10%. A full charge lasts an insane amount of time, like 60 straight hours in GPS mode. I literally never need to think about the battery level on my watch. As long as I plug it in once every week or two, I've always got plenty of battery for anything I'm going to do.

The reason I mentioned that I came from a Vivoactive 3 Music, is that it has a similar battery life to the smaller 6S. The opposite end of the battery life spectrum. And I hated that battery. I would charge it to 100% in the car on the way to a hike, and after 8 hours it was dead as a doornail. IF I started my hike with only 50% charge, forget about it - I'd be lucky if it didn't die before my first rest stop. Had many of my best hikes not get recorded because the battery died mid-hike, and that was what made me decide to never again settle for a lesser battery.

With my 6X, I get a huge amount of data on my screen, and I can go out for any length of hike without worrying whatsoever about what my battery % is at beforehand. The value in that is tremendous for me. Even though I still carry a battery pack for multi-day trips, wouldn't it be nice to not have to not need it?

As for the size, I have very small wrists... been wearing my 6X for 4 months, and never once felt like it was too big. It's really not as big as you might think - I recommend giving it a try at a local store before you decide. I think the benefits outweigh the... well, weight. Your mileage may vary.

What it comes down to for me is, while sure I "can" charge my watch on the go during long hikes, it's really nice that I don't need to.

My choice was actually to spend quite a lot extra and get the MARQ. I have quite slim wrists and had the F5 earlier. Before that I had the huge Suunto Ambit. I did look at the F6Xpro or solar, since two drawbacks of the MARQ is the sapphire crystal and the screen size. As I do trail running or MTB, reflections are disturbing and the size of the map a bit small. But given that I rarely do sessions longer than a day, battery is good for me. And on longer outings I bring a charger. 

For day to day use, the MARQ is really nice. And it is quite similar in size with the F6, with the F6 having a bigger screen, whilst the MARQ is more solid in its feeling with the all titanium case. 

So, my decision was either the F6x for maximum usability outdoors. Or the MARQ for nicest all round use. Different price level, I know...

Sorry - I meant 17.5cm of course, corrected it.

C.sco I usually do plan ahead if I'm outdoors, so charging beforehand isn't a problem.

It sounds a bit dramatic as you explain it, the 6 sapphire still has a good battery life on it's own.

What I want to avoid is carrying this huge battery if I only really use/need it in 5-10% of cases.