>>4095859At the same ISO, m43 will typically be noisier than APS-C, which is typically noisier than FF. The X-T5 will almost certainly be less noisy at a given ISO than the OM-1.
You have to consider your lenses too though. If you got OM-1 + f1.4 lens, you could shoot at half the ISO of an X-T5 + f2 lens, and end up with similar or maybe even less noise. If you got the OM-1 + f1.2, you'd get even less noise, but then you could get X-T5 + f1.4 and get even less.
