Eurasian blue tits like eating young buds, various insects, and used to go for the cream on milk when foil-topped bottled on the doorstep were still a thing.

Also, here's a Long-tailed Tit - this is what I'd originally thought was a young wagtail.

Apparently they can take three weeks to build their nest, using moss and spider silk for structure, lichen on the outside, and between 1500-2000 feathers on the inside. No wonder it takes them so long.

...and leaving a trail of really, really pissed-off spiders in their long-tailed wake.

What are you shooting with these days?

A heavy-but-versatile 50-500mm Sigma lens on a full frame 24MP Nikon D750.

These are some really lovely tits, Peter.

Hey Dan, long time no see! :D

Thinking of making the step to full frame, but can't quite convince myself yet.

What sort of photos do you take, and what have you got at the moment?

Sony A6000, previously had a Pentax K200D.
Looking at the Sony A7iii.

Landscape and some nature usually. Have quite a few old manual lenses I like to use too.

Also want the much improved video.

When I upgraded it was an easy choice - double the sensor resolution, better sensitivity, low light handling, rear screen, etc.

I don't remember if I was aware or placed much import on the depth of field benefits from the bigger sensor, but of course shots like those tits would be less impressive without it.

On the other hand, for well-exposed landscape shots the sensor is less significant.

I think I'm more so trying to talk myself out of doing it.

I can see lots of benefits, but the drawbacks are...
Cost - significant, but would hope to last me 5+ years before I feel the need to even consider looking for a new camera.

Size - the reason I bought the A6000 was because I stopped enjoying taking my K200D out with me as it was too big and bulky. But when I didn't I then regretted not having it. So I went for a mirrorless APS-C camera. Going full frame (even mirrorless) pushes me back towards a larger camera. Though I am much more enjoying photography again these days so I'd hope I'd get past the size.

Yeah, I'd say size is something you get past - though I did get myself a decent compact to always carry around for similar reasons, but having the choice I find I don't use it as much as I might have. Still enough that I'm glad I have it, but without it I'd regret shots that I otherwise decide are not worth taking. I always take the D750 when I know I'm going to be doing photography.

I do think in your position I probably would wait a year or two for the next generation before upgrading, (unless you're specifically hitting the boundaries that the A7iii definitely overcomes).