I can't speak for the 4k 5-20, but I did have a xs 2 5-20 and it was great. That being said, when I upgraded to a 4k I went with the 3-14 just for the better field of view on native mag. The biggest hinderence with night time range is the stock IR that comes with. If you want to be able to see a long ways out, get an upgraded IR Illuminator. I also can't say that I have had any experience with the Bushnell optic you mentioned.
When I had my XS 2 5-20, I was able to see fence posts about about 425 yards with the included IR Illuminator. A lot of folks have issues with being able to get any kind of acceptable range out of the included IR, but after a bit of tweaking with it I was able to get the results I mentioned earlier.(with the xsight 2 5-20)
An upgraded IR will be far better. THis video I'm going to link shows the 4k 5-20 paired with a Sniper Hawg Lights Coyote Cannon @ 850 yards. This is a BIG light, but they are fricken sweet.
I have a 66LRX from SHL with a red emitter and absolutely love it. I can easily see 650+ yards with the 66LRX.
The night viewing range is going to be fully dependant on the quality of the IR Illuminator you are using.