Hi.

If you're using Lightroom, see where it's storing its catalog files. I think it automatically goes for the C: drive, and can take up a lot of space. They don't make it easy to redirect the catalog storage, but it can be done. (Unfortunately, I don't remember how I did it - had to look online, I think.)

A Sigma 60-600 mm lens (with help from my wife and accumulated credit card rewards points).

It's a heavy beast! I like it, though.

I have the 5D Mark IV and the 90D, and I shot for several years with both the 7D and the 7D Mark II. Like you, I mostly do nature, wildlife, and bird photography. I also do adoption photos for a local cat/kitten rescue.

The 90D is an improvement in some ways, but overall the 5D Mark IV is a better camera. It has far less image noise and performs much better in low-light conditions. I do not at all miss the few frames/second greater speed of the 7D and 90D. The 5D is much more rugged, too. After shooting with it, the 90D does feel a bit like a toy - a well-built toy, though.

In terms of noise, I can often shoot up to ISO 3,200 with the 5D Mark IV, sometimes even higher, with very little noise reduction needed. With the 90D, I find myself moving the Luminance noise reduction slider in Lightroom up to at least 30, even at ISO 100. By the time I get rid of the 90D's noise, I end up with images that are far softer than I like.

The one place where the 90D shines for me, and the main reason I'm keeping it, is for macro photography. When you have to get the camera low to the ground or in other awkward positions, that tilting rear display is a back saver! And the image quality of the 90D is good. If I'd never shot the 5D, I might not even be complaining about it now.

I don't have personal experience with the 5D Mark III, but people I know who use it rave about its image quality and low-light capabilities the way I do about the Mark IV.

I agree that if you can find a refurbished or gently-used 5D Mark IV, you'll be happier for a longer time. There'll be no reason any time soon to want to replace it. The 5D Mark III would probably be my next choice. The 90D would be a step up from the T3, though.

I just made that exact switch myself a week ago. I've only shot about 150 photos with the 90D so far, but here are my initial impressions. I'd used both the 7D Mark 1 and the 7D Mark 2 before that, although my main camera now is a 5D Mark IV. That 5D beats both the 7Dii and the 90D for low-light photography.

I think it depends very much upon what kind of photography you intend to do. For low-light and indoor shooting (without studio lights), the 90D is a little bit of an improvement over the 7Dii. It has a higher ISO range and slightly less image noise.

Outdoors, in daylight, you might not notice a lot of difference. I thought the 90D's 32 MP sensor would be a vast improvement, and it is better, but it's not all that much better that I can see. And even though it has roughly 60% higher pixel density (pixels per square inch) than my 5D, in side-by-side comparisons between those two I noticed the noise difference more than any difference in detail.

For me, the place where the 90D outshines both the 7Dii and the 5D is in macro photography involving odd angles and contortions. That rotating rear view screen will seriously save my back when shooting near ground level, etc. That's the main thing I'll be using the 90D for, and the main reason I'll keep it.

I'll be giving it a better workout with general nature photography (birds, insects, etc.) today. I've shot some birds at home with it with good results, but haven't taken it out in the field yet.

My main complaint with the 7Dii was noise. After seeing the 5D's images, I couldn't go back to it. I had hoped the 7Dii would be an improvement over the original 7D noise-wise, but it wasn't. I think the 90D is a little bit better than the 7Dii in that department, but it's not nearly as low-noise as my 5Div. Even at ISOs down to 400, I find myself doing noise reduction in post-processing on the 90D's images.

Build-wise, the 90D is pretty good, but it's not as solid as the 7D, and I doubt it's as weather-proof.

#1 for me. It's more dramatic.