Welcome to the forum.
30 KPH is normal for an ebike, and the legal limit in many places.
40kph is fast but reasonable for an Ebike. Expect to spend $1500-2000 for a bike that can maintain that. You can half a$$ it and build it cheaper with half a$$ parts, but expect it to be a half a$4 bike with half a$$ performance .
60kph isn't an ebike anymore. That's motorcycle speeds, and you're going to quickly find out why motorcycles are built with thicker, heavier duty parts. You can build an ebike that will do this, but if you have to ask someone else how, then you don't yet have the knowledge or experience to do it without killing yourself.
So telling you would be like handing a loaded gun to a child, but then our gene pool needs some chlorine, so here goes.
A Crystalyte HS3540 running 72 volts through a 18FET controller should get you north of 60kph.
Do it right, it will be awesome. Do it wrong, you'll be street pizza. If you want to do it right, start with a basic ebike that will do 30-40kph. build it to last, and run it until you have enough experience to know why questions like yours get reactions like this from most people. Then you'll live long enough to think 60kph was a boring goal anyways, and be after more speed.