what is an engines rated speed?

I am confused. My Wolseley WD2 has a brass plate which states '1.5 bhp at 700 RPM'. By turning the speed control I can get the engine to rev from 650 - 1000 RPM. So does this mean that 700 RPM should be the engines maximum speed when driving equipment? ie water pump places load on engine, revs drop, increase speed control until 700 RPM is reached.

It means that at 700 rpm it is kicking out 1.5 hp. On a rally field all you want is the engine ticking over enough to run what ever you are driving, especially if you are a Scot or a Yorkshireman..........less fuel!

.....and fast enough to ensure proper splash lubrication by the oil, so not too slow.

Thanks guys, I shall stop worrying about it then!