Most marine diesels max at about 3000 rpm. Based on Beta's specs for the BD722, max rpm is 3600 rpm. Was this under load or in neutral? A diesel should not be run at high rpm unless under load. When running your best rpm is probably between 2500 and 2800 rpm. You also probably won't gain more speed past this - just dig a bigger hole in the water and burn more fuel. Reserve max rpm for short runs when you really need it.
I'm not sure about the glow plugs as I've never had a diesel with them.
If you smell a lot of diesel combined with the advice to remove 30 year old steel tank I suggest you have that work done asap. Unless you have spilled diesel fuel while changing filters or bleeding lines there should be no diesel smell. A diesel is a closed system with injectors and the only openings the engine has to the atmosphere should be the tank vent and the exhaust. As I write this I am sitting at the salon table within 6 feet of a Yanmar that has no smell whatsoever.
If you're not sure about the operation of your diesel get a good book like Calder's book (shown below). It might be a good idea to pay a good mechanic to spend an hour going through your engine and systems on the boat to learn how to operate them properly.