TomD
"Is everybody going to have to buy a water-cooled slow-speed grinder to use these 'new' steels or risk ruining them even though the operator is relatively skilled at the grinder?"

It's actually the reverse. The old steels can be tempered at low heat, domestic oven heat. This means it is easy to over-heat them and end up with a softer tool that the manufacturer intended, though if you love soft tools, no biggie. The flip side is that you can reharden them at home because they are easily heat treated with workshop gear, the main limitation most people face being a tempering oven that will operate at high temp, but isn't needed for plain steel.

The other thing is that certain jobs will heat the tool so much they draw the temper. Since tool steel is generally more about making cars than say milking stools, this can easily happen. So we have HSS which is designed to work at any heat, pretty much, worst case it just gets harder.

So the "new" HSS steels are the easy to grind without worry steels, the old steels are the worrisome ones. Though skill will conquer all.

When I bought my original grinder it was an 8" 1800 model, and it is still chugging. When I much later got into metal working heavy iron, I think I figured out the whole 6", 3600 rpm, gray green wheel thing. Those are designed to burn out with friction lathe bits, etc... in HSS. Or with different wheels grind carbide. Those should probably never make it into a woodworking shop, though they do work with a light touch. But to me they are designed to burn off the metal with friction, they are capable of 4x the heat. And the extra speed makes them 4x as dangerous if a wheel blows.