Glass wise on the Sig vs the Vortex Fury....to me, it's a wash. They seemed the same to me in the couple of times I got to compare them. Other folks I have talked to feel the same. Basically, the glass in the 3k BDX is about the same as the Vipers, but a little more natural color balance IMO.
As far as ranging goes, I am working on a review on these, but they are very strong. Their only real weakness in this regard is the sensor/reticle alignment, a weakness shared in some capacity by most RF's. But once you figure out where your sensor lies in relation to the reticle, you can pull off some pretty impressive distances.
It is very fast in re-ranging, and it's re-connection time to a Kestrel is super quick. Using the Kestrel with it is really cool as well, it's where it is at it's best as it does not have internal environmentals. But even just loading your curve and environmental conditions in through the phone and then running it, it gives a pretty solid solution via AB Ultralite, though you definitely want to true it.
I am running a VX6 on my main rifle, so like you, I am not running the BDX scope on that gun, but we did swap my son's VX3i out for the BDX, almost done with the review on that one. I was actually impressed with the scope, better than I expected in terms of overall performance. I'll say this, the BDX integration is impressive. I thought it was kinda a gimmick when Sig first showed it to me, but since using it this year and it proving it's value through it's speed on an Aoudad hunt in January, I am impressed. I am not going to give up my VX6 level glass for it, nor my Zeiss FL's for the binos, but this system in a Tango 6 scope and Zulu 9 binos might have me rethinking that, I have been that impressed.
The binos are not perfect by any means, the diopters could use some locks, and the reticle/sensor relationship could do with some tightening up. But the glass is better than I expected, the RF is very strong and fast, and the data exchange system has had real value for us, even just it's connection to the Kestrel.
HTH, feel free to ping me if I can answer any additional questions.