I have used the XTR. Can't help with the Viper Vortex. Burris XTRs are tough, track well, and have good clarity. The SCR reticle is nice and simple to use. I have used it for hold overs out to 600 yards with great success. I did experience some downsides. They are pretty hefty and large. Also, during a comp, my shooting partners XTR completely washed out in the sun. I could not see the targets. It was a partnered switch rifles event. He saw the targets fine with my SWFA. It could have been a sun shade issue (lack of one), or my buddy was at a different angle to the sun. He was about 4 feet to my right. To say the least, it did frustrate me. If you bought one, I do not think you will be disappointed. It hits hard for its price point.