This really is a bit of a minefield. One thing worth mentioning is that there can be some incredible seeing in Melbourne, I'm talking top shelf stuff. Take this image of 47 Tuc.
Full Resolution
It has been taken with a Mewlon 250 at F/10 with an ASI094 which results in 0.4"/pixel. This is about 40 minutes of 120s exposures, the final stack has a FWHM of ~1.4" with the best single exposure being closer to 1.1" seeing. That's about 3-4 pixels at 0.4"/pixel. Now 0.4"/pixel is a bit over the top but the best single sub I've managed from Melbourne as been 0.96" so that's a fraction under 1" seeing from my suburban backyard.
Don't get me wrong, I've had terrible nights of 4" seeing but my average is around 1.5-2".