>>3657872First off, resolution NEVER comes at the cost of poor low light capabilities. How a sensor deals with noise is inherent to its physical size and properties. You cannot compare the noise of the two images directly, but would need to downsize the higher resolution image to the same resolution to compare it. This averages out noise in the higher resolution image. See pic related, the 1d only has a slight improvement over the 5DSR. (As a reference, the green 38db line is seen as pretty much undetectable by the eye)
>more durable build quality>more physical controls>Native EF mountThis definitely means a DSLR, now you should think whether you are willing to sacrifice an OVF for this, since I can imagine that for your portrait photography, focus peaking is quite useful.
Since portraits and architecture are your primary use cases, I'd say go for a 5D type camera (mark 4, DS or DSR are probably all fine). Even the mark 4 has probably plenty of resolution for you, although if you want more that just leaves the DS and DSR.
The thing is, the 1D series is not made for the kind of photography you do. It is meant for high output, fast paced workflows such as sports photographers, or for people who need an exceptionally durable camera such as wildlife photographers or journalists. The 1D is also almost double the price of the 5D you are looking for. If you really also need that speed, buy a 7D or something on the side for that.
Yes, you cannot have both higher resolution but keep smaller file size, but you can always downsize your files, never upsize them (and get data that was not there). You could easily make a photoshop script that downsizes the files to a lower resolution for you anyways, or if you really want best of both worlds, get a 5DSR for high res stuff and video, and a regular mark 4 for high volume/backup body. Even that last option is nearly identical in price. Or go for a mark 2/3 second hand as a backup/high volume camera.
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