So I’ve a EOS 40D which is starting to show its age, in good physical condition and in daylight it’s awesome but when my phone can take better low-light photos than the 40D with a f/1.4 lens I know it’s time to either retire the SLR, or get a new body.

Obviously I’m going for new body.

I’m not made of money so will happily buy a used body. Looking around, the 70D looks like a good compromise. New enough that it has a good sensitivity, does video, articulating screen, still has lots of buttons (I love the focus point jog dial and really miss it when using my wife’s 450D) and you can pick it up for £500. Or should I up my budget and look at the 77D/80D/whatever xxxD there is now?

Odd Ive not noticed my 40D slacking in low light!

You can pick up a used 6D mk1 in good/excllent condition for about £600.

I’d go 7d (or 70d if you prefer the video gubbins and articulating things).
The light sensitivity on either will be better than a 40d, but the focusing system improvements will outclass a 40d to a much greater extent.

Trouble with going to 6D is that it needs EF lenses. EFS will not work.

Yeah I don’t fancy buying new glass and two of my three lenses are EF-S which noticable issues on a full-frame sensor.

Trouble with going to 6D is that it needs EF lenses. EFS will not work.

Is there not an option for a crop mode until you’re able to replace the lenses?

The light sensitivity on either will be better than a 40d

It’s a small point but ISO performance has nothing to do with ‘light sensitivity’, it’s all about applied gain and signal to noise ratio. SNR firmware has come along a great deal recently whih is why more modern cameras perform so much better at higher ISOs.

Is there not an option for a crop mode until you’re able to replace the lenses?

If the idea is to eventually replace both body and lenses it might be worth asking if doing it this way, which means locking in to a Canon system, is the way to go. Could be better long term to rethink which system is most fit for the OP’s purpose.

Could be better long term to rethink which system is most fit for the OP’s purpose.

If it were my money I’d buy a Fuji and an EF to X adapter.

Is there not an option for a crop mode until you’re able to replace the lenses?

When they were launched EF-S lenses had different dimensions that impinged on where the mirror would be on a full-frame camera. The newer full-frame bodies may have been designed to be compatible but it sounds unlikely.