I actually ended up being able to test it myself. I was planning on keeping only one of them, so keep in mind I was really picky during the test.
I would say the 950 XL worked better on continuum, but depending on tasks, the difference may not be significant. Webpages containing more media content loaded quite a bit faster. Depending on webpage, the loading time difference can go up to 2 seconds (doesn't look much on paper, but it's quite significant in real life)
I also noticed that the 950XL seemed to do more background tasks (or does it faster). Take edge for instance, if you open multiple tabs at once, the 950XL will have them all loaded eventually, more like the experience in real computers, but on the 950, it almost seems like it only really load the tab when you're actually on that specific tab. Also, on the 950XL, I was able to use mouse scroll sooner after the page loaded (I was able to just plug in the wireless dongle of my logitech keyboard and use it in continuum immediately. Pleasant surprise!). On the 950, you'll have to wait longer. However, you can almost immediately scroll using the phone as trackpad on both the 950 and 950XL, so I'd imagine this issue being fixed in future updates.
Also, as one reviewer pointed out, the 950 runs hot in continuum, but the 950XL was warm. Installing the app "disable screen" helped a lot and made the 950 cooler, more to the side of warm.
All in all, the 950XL is faster, as expected, but if you don't compare them side by side, the 950 is still pretty smooth. They both run quite well with all the universal apps (pretty identical performance between the two in this regard. Well, there may be a .25 second difference between tasks, but only noticeable when you compare them sided by side.).
I ended up returning the 950XL due to its size and some other personal preferences on the 950. I like the fact that MS equipped the two phone with almost identical specs (especially same camera) as I've been looking for a smaller phone with good specs. I tried both phones in continuum extensively for a week as my desktop at home, and I actually found both of them pretty convenient and capable. I have not turned on my desktop since.