Pre-mix.....
The reason your seeing threads on pre-mix is because in the older engines, you never know when that oil injector pump is going to go out. If it wears to the point that volume drops off, then you'll lean the oil mix out and burn a hole in a piston. If your oil pump goes "out" and your not aware of it, you lose the engine.
Most people who aren't super mechanically inclined, choose to premix. It gives them a sense of security that it's one less thing for them to worry about, that can be terminal should something happen.
I have a 1997 model 787 and I still use the oil injection. But I do a volume test and inspection once a year in the off season.
If you already have the oil injection system installed and want to continue to use it, if it's over 10 years old, I'd recommend that you do a volume test on it before you put total trust in that pump.
You can read the plugs after running 15 minutes at WOT. At the end of the 15 minutes, pull the lanyard so the engine dies out at it's WOT setting. Then, look at the plugs. If they are within the specs of good mix and fire, I wouldn't worry about it...............:cheers:
Here's a link to my thread "Snipes Korner"......you'll find a thread in there on the conditions of spark plugs and what they are suppose to look like.
http://www.seadooforum.com/showthread.php?t=4151