I'm a Nokia Lumia 1020 owner. And when the groundbreaking 1020 came out I was in heaven. It was (and in my opinion, still is ... at least for those of us who want to delve into photography and video a little deeper than the average user) the best cameraphone around.
If you really care about photography you ARE in a real difficult predicament, I must tell you.
First of all, allow me this advice: STAY AWAY from the Xperia Z5. OR any other Xperia phone, really. It will NOT reach the underground over which the 1020 stands. I know this, I used a Z3 Compact for a year (it was the phone I jumped to once Nokia went away from phones). I absolutely loved everything about the phone except the camera.
When the Z3 came out, it easily matched the 930 but it never matched the 808/1020. When the Z5 came out, the Z3 had already been beaten by the LG G4, the plethora of Galaxies S6 variants and in some cases even by the Nokia 930 post-Denim. The Z5, unfortunately, kept doing the same mistakes the former Z3 did. The Z5 has a very very sub-par camera, which is something that should make Sony feel ashamed. It still lacks OIS (for aesthetic reasons, as I was told directly by a member of Sony's design team), the software is still a post-processing mess and Sony's so called "manual mode" is a joke, which doesn't allow you to tweak almost anything. No shutter speeds, no manual focus and now you can't even adjust the ISO if you decide to shoot at full 23mp resolution. Oh, and forget using another camera from the Play Store because Sony kept all the camera2api that Google introduced in Lollipop locked on their devices (probably so you wouldn't get another camera app and realise how bad Sony's actually is).
And don't pay attention to what Dxomark says, their results are all forged.
Now to your current predicament:
The 950/XL has a great camera, sure. Better than the Nokia 1020? No.
Is the camera on the 950/XL one of the best out there? Yes. Is it the king of cameras? No.
When it comes to photography, the camera currently to beat if the LG G4's in manual mode and the S6's in auto-mode. So, since you own a Nokia 1020 and you care about photography, I'm going to assume here that you care about manual controls. In that aspect, the G4 if the only one that offers you the same experience as a Lumia and some extra things Lumias don't do (like, for example, showing you the result of your tweaks in real time on the viewfinder before you take a photo and give you an actual spectrum in the WB section). The S6 lacks a bunch of manual controls (although it does offer some). The only downside the G4 camera (as well as the S6 btw) has is that it lacks a dedicated camera shutter button.
Here's the G4 manual mode interface so you can compare it to the Lumia
Now the question is how much do you:
1 - Believe in the future of WP10
2 - Need a proper app ecosystem.
I personally wouldn't advise anyone to buy a 950/XL. And not only because of my known despise for Microsoft Mobile. The reason I would do it is because these phones are just to entertain WP fan(atics) for the time being. Windows Phone flopped. "Windows 10 Mobile" is just Windows Phone 10. It has no future. Microsoft knows this. Which is why the so called "Surface Phone" is happening. That one is expected to be a true PC in your pocket (ie. be able to run win32 programs). But even the Surface Phone will not, I'm sure, be camera-centric. In fact, I'm not sure it will even have a camera worth writing home about. Because it will be truly focused on productivity and not photography, since that's the path Microsoft is taking.
There's the UWP thing, sure, but honestly? I think this is the one time Ballmer is actually right. Universal Windows Apps will not succeed. Not in solving the app gap and "saving" Windows Phone 10/Mobile at least.
My advise, if you want a great smartphone with a great camera, is: jump to Android and get yourself an LG G4 now (or wait 6 more months tops and get a G5 which should already include the tech LG will be licensing from Nokia). As for it being Android, don't worry. You will, as the OP said, be able to keep your Microsoft ecosystem intact on Android. I did (well, except for the things Microsoft itself ruined like the Outlook.com app which, however, you can replace with another email app of your liking and still use Outlook flawlessly and more recently OneDrive).
By this time next year you should have a clearer picture about the path Microsoft is taking, you should have seen the "Surface Phone" and you can decide if it's worth your time and money to return to a Microsoft mobile operating system (assuming WP10 won't be killed off in the end of 2016 which is something I *suspect* will happen as soon as the Surface Phone is announced.
Currently both WP10 and the Lumias 950/XL, as pretty much every honest reviewer said (including Rubino) is really only for fans. And I would add "die hard fans" or "borderline fanatics". Those people whose allegiance is first and foremost towards Microsoft, regardless of what they do with the operating systems or what their phones offer (and note that I do not condemn those people because I have always been exactly like that towards Nokia...which is the reason I ever used WP for 3 years as a daily driver in the first place)