It's a good question, and one people debate often with regard to 2-stroke engines..
one school of thought is ' run it lean, keep it clean '..
the other is ' oil is the life blood, run it a touch rich '..
I personally, have raced 8 and 10hp mariner's in my boat for a few years now - and run wide open throttle for hours on end..
for this purpose, I run my oil rich.. from 40:1 right down to 25:1.. and I've never fouled a plug..
I run full or modified synthetic.. and have experimented with oils from Castrol R30 castor to the TTS racing oils, and also with MOTUL 2 cycle engine oils..
I found a few differences, but namely that the motul synthetic ( red oil ) ran really well.. displaced the heat exceptionally well.. didnt foul and had a lovely smell.. ( yeah i know, it's weird - but I enjoy a nice 2 stroke smell ) - also didnt look like gorillas in the mist from the smoke..
You may ask ' how does he know it displaced the heat well ? ' - well, I run a line from the discharge - up and through the tiller - so that the output runs across the back of my hand - this way, I can monitor the engines temp.. if it's too hot for my hand, I need to drop the motor in the water a little deeper.. or back off a bit on the throttle.. ( we jack our motors up on a sliding transholm for speed and depth clearance )