I would have to go with the 80's. The 2.4's are still really quick with the right setup. Something which trickled over from the 70's, but the 80's really saw the rise of, is the 3cyl yamaha for roundy round - my neighbor was the person to first break 100mph on the water with less than 100hp. There was a lot of innovation in the 80's as well, by people like the Pughs, Reynolds, Orans, etc - lots of world records which have still not been broken came from the 80's.
Boat racing was not what it is today, which is too regulated, both from the racing and viewing perspective. When I was young (in the 80's, when I was born you bunch of old hillbilly's (Hensley)), I remember watching my neighbors test boats in front of the dock. People were pushing a different envelope then. On the 4th, Budweiser would sponsor the races in Kingston, and you could park along the bluff and watch (and smell) racing all day long. What a time. Now, Budweiser can't sponsor jack in Kingston (which I realize has nothing to do with engines), and the sport has declined on the spectator side of things.
Anyway, my beef with EFI. What did it "fix"? Mercury locked it down so tight, and the EFI boxes on the 90's Merc's are so stupid/unintelligent about the running condition of the engine, they're basically just dumping fuel into the motor like a carb, only factoring a couple of pre-iginition variables and utilizing timers for warm-up mechanics. Merc saw this "innovation" as an opportunity to grab the consumer by the undercarriage and not allow us to tune our own motors, except mechanically. A normal person couldn't even hook up to the diag port for a long time, and the subscription for the DDT was outrageous for dealers. Eventually Tony B did make an ECU with a tune-able fuel map, but it is still based on antiquated technology, relying only on setting the injector dwell time based on ignition, and not actually changing the ignition to suit conditions, as any other decent ECU does. Nikasil is junk for most average hot rodder/racer groups. And the differences between the 175/200/225's and 260/280/300's - what a joke.
I think I've steered off the tracks somewhere
. So carb motors, and the events which they drove, the records, the innovation, all happened (mostly) in the 80's. I'll have to save my lower unit conversation for another day - not enough time in the day to bash on the sportmaster and why it sucks.
Let me know what you think