Kinda late to the party but I'll share my thoughts.
These comparisons are always hard because there seems to be so much variation from one specimen of a supposedly identical scope to the next. Kinda like OEM barrels, SHOULD be manufactured to the same specs, but there are factory barrels that shoot much better than other factory barrels. Same gun, same caliber, but one will shoot lights out and the other is a flyer factory. Scopes are the same. One really good X50 next to a really bad Sightron, or vice versa, skews opinions-call it the statistical dilemma of N of 1 studies or comparisons. If a guy could look at 10 different X50s and then 10 different Sightron's it'd be a more valid comparison, but you're talking about $20,000 worth of scope there, so not many are ever going to be in that position.
Anyway.....
I have an X50, one of the first few in the US. I think I've had it for close to 3 years now. (The earliest ones don't have a mark @ 16x but I've been told the more recently manufactured/imported ones do.)
I debated a high end (for me) high mag scope for field target for quite a while. Knew I was wanting to spend in the $$$ ballpark of the two scopes OP is considering, Sightron vs X50 so they were on my short list. Prior to pulling the trigger on the X50 I was fortunate to have the chance to look through a friend's X50 as well as the big Sightron at the same match, in the same light, at the same downrange items-about the best side by side comparison I could possibly think of. My conclusion was that they were both about equal in clarity, but the depth of focus was tighter on the X50 than on the Sightron. I also liked the reticle on the X50 better than any of the Sightron options.
So, I bought an X50. And started winning monthly FT matches. This FACT is part of my argument that it's not always the indian when it comes to the philosophical debate of indian or the arrow. I couldn't win until I spent enough. Same shooter, but with capable equipment. That's an aside though.......
Back to the comparison of the X50 and the Sightron. When I first got the scope I wanted to gain confidence in it so screwed a section of pic rail to a block of wood that I ratchet strapped to a big heavy butch block in a place I could see out to my back fence (around 52 yards away at that house). I put that scope through everything. Cranked and twisted and box tested and let it sit out in the hot uninsulated garage. I could not induce any scope shift in how it ranges or tracks in that testing.
Mounted it up and zeroed it. Tried a few more experiments with it left in the hot garage and also direct sun and couldn't cause any shift in range by focus or tracking. Also could not induce any problems.
It lives on my serious FT gun and does what it should. I range at 50x and take my shots at 20x.
For the bad.......The comment above about it getting a bit dark and even hazy around the edges at 50x is true. It does stay clear in the middle of the scope though. The scope caps supplied with the X50 aren't very high quality. The supplied sun shade is also really thick aluminum and HEAVY. I don't use the sun shade b/c it's heavy enough to shift the balance of my gun in a way that I don't like. Also as mentioned above, the FT version (the one I own) is not the greatest for long range shooting-as distance increase, image quality goes down. It's useable for 100 yard paper punching, but not ideal.
In summary, for the purposes I envisioned for a high power scope (field target) my specimen of the Falcon X50 has been superb.
