35mm, file tread, run it around 45 psi. Thats the short answer if you cant be bothered reading the rest of this. But the longer answer is more useful, because the wrong tyre on the wrong Perth path is how you end up walking a bike home with a pinch flat, and I've done that more than once before I started paying attention.
I rode the gravel bike last weekend with the Sunday bunch out past the usual stretch near the coast, swapped onto the old hybrid midweek for a servo coffee run, and the difference in how each bike handled the same ten kilometres of path told me most of what I needed to know for this piece. Gravel vs bitumen tyres isn't really a debate about which surface is better. Perth doesn't give you that luxury. Most routes worth doing mix both, sometimes in the same five-minute stretch, and your tyre choice has to cope with that rather than specialise in one or the other.