fenix 6 pro run distance accuracy ??

The question is, how many % deviation compared to real distance (and speed/pace) should we accept? 0.5%, 1%, 2%, 5%, 10%? My old Garmin Forerunner 310XT was more accurate than my new Fenix 6X Pro Solar Titanium. Should we accept that we need to wear the watch on inner wrist while running (to reduce deviations)? 

Your old 310XT (like mine) has a SIRF chip. Much like the 305.  Broadcom bought SIRF and licensing and lawsuits took it out of use.  The tracks didn't look as nice but the distance reporting was fantastic.  Ironically from my 705 bike gps, I surmised that the distance accuracy came from inaccurate counting of stray reads, making it accumulate to the correct distance.    The newer watches use Sony due to power consumption but the Sony chip hasn't quite been ready for prime time.  The MediaTek chip was used before the 6 and it wasn't stellar either.

I love the Garmin speed sensor because you can take a 2 -5 mile open road straight stretch and calibrate your wheel size almost perfectly.  The Stryd has been fantastic and I have no idea how over 4.5 miles or more of trails, it will come within hundredths of a mile within each run and true to the reported distance.

Just think.  If Garmin said you could get a Fenix 6 that would report more accurately than any other watch or handheld device but it was 200 more to get it, would you buy it?

You did not reply on my questions.

No, i would not pay more to get a more accurate watch. I expect that at 10000SEK watch should be better than an 10 years old Garmin Watch. Garmin must fix this problem. Its not acceptable.

I sold my Stryd on eBay because it wasn’t doing anything better than my Polar Grit X, especially on trail runs. A Footpod works great if running at the same pace and on flat courses. It doesn’t work as well on hills, where beside the ascent / descent, also a pace change is involved in the equation. I rather have an extra 450$ watch like the Grit X than a 220$ foot pod. Once again, I love the Fenix 6 as a daily driver but after investing about 1,000$ on watch itself, nylon band to be used when I don’t run and extra topomaps (i run in the US as well as in Europe) I would like to see a better distance measuring on the watch itself, especially after I found out that with the download / upload trick the metrics are pretty much correct. 

Putting features aside - 
If you want a watch that has the distance accuracy of the older SIRF chip watches, you have no options.  So if you run on the roads with minimal twists/turns, minimal high buildings, etc. you can accept little if any decrease - less than 1%.  If you are running trails with switchback and heavy canopy - You won't find a current watch that is doing it well.  so anywhere between 2-7% depending on run/bike and the trail.  That's my experience.  The new Polars, Suuntos are just as bad from what I read but I can't tell you that first hand.  Forgive me for not answering.  I thought it was rhetorical.  I fear your expectation on the existing technology/power consumption, etc. is probably going set you up for disappointment.
All I can tell you is that investing in the Stryd and Speed sensor keeps me from checking it and has me very satisfied.

I don’t know if I got lucky, but my Polar Grit X and the Polar V800 are always within 0.5% of the actual distance. I have also a Garmin FR610 with the old SIRF chip and for distance measuring it’s better than the Fenix 6, which doesn’t make sense because its value is 50$ vs a 1,000$ current production top of the line watch. 
I have also a Garmin 735XT which is as bad as the Fenix 6, I had a Fenix 3, as bad as the Fenix 6, a Suunto Ambit 3 as good as the FR610 and a couple of Apple watches that are fairy good for measuring distances but IMHO they aren’t appropriate for the avid runner. 
To be honest, if I could have just one watch, I would dump the Fenix 6 and I would keep the Grit X as a daily driver, but I like very much the style of the Fenix and the additional features that I don’t have on the Polar. However I’m sick and tired of all its glitches, not to mention the Garmin platform who is down every other week. 

I bought the Fenix 6 pro about 3 months ago and was excited to start my new training regime, after reading about all the features, it seemed there was nothing this watch couldn’t do!!! 

..the reality is this watch is a really expensive wristband..the Optical wrist monitor shows as high as 180BPM on an easy run (actual pulse is around 135) on my old Apple Watch...so that function is just laughable.

Because of this all the other features ..VO2 , recovery , training and overtraining information and predicted times have no use either.

GPS is mediocre and has been as much as a half mile out (short) over 10 miles, sometimes it’s better than this but no two days are the same so can’t depend on that fully..

.I have tried most things to try and sort this myself by reading suggestions on here but if your paying a premium price you shouldn’t have to jump through hoops to try and sort all the things that are wrong with this watch..that’s Garmins headache

I’ve been running for 30 years and regularly run over 100 mile weeks during my base training phase so I need these functions to work for me..i have never tried Garmin before but was impressed by all the features the watch promised..

if someone from Garmin reads this review could you at least please help me out here and send me a HR chest strap, that way at least I can get some use from the watch..£650 for a stopwatch just isn’t on.

Basically, for most of the users the Fenix 6 it’s ok, it’s a nice looking watch with a lot of features, most of them are totally useless since anyhow you need to have a smartphone to have them working, so why not looking directly at the phone (weather, calendar and so on...) and the Vo2, BPM, recovery and training suggestions aren’t reliable because the GPS metrics aren’t accurate enough. Therefore for a serious runner who cares about accurate metrics to program his / her training the Fenix 6 it’s rubbish. End of the story. 

Yes, the distance on GPS track produced by Fenix 6 is always longer than the distance reported by the same watch. That has been my observation as well. The difference is  greater when running on trails under tree cover - occasionally more than 5%. The easiest way to see distance on the track is to do distance correction in Strava.