The most reputable octane boost is Torco Accellerator. Hard to find. Toluene works well, too. I've run up to 30% toluene for testing, to see if my knock retard would go away. You can get that at paint stores. Here's some info on toluene and other boosters:

http://www.elektro.com/~audi/audi/toluene.html

I wouldn't think some knock retard due to the octane being a little low on a stock motor would cause a 'fall on it's face' kind of power loss, though. Certainly worth trying, but that kind of issue will be ignition, fuel starving, or valve float IMO. I'd start with a fuel pressure guage first, and see if it drops when the problem occurs. Then ignition. Rule those out first, and if you still don't fix it, suspect the valvesprings are worn out.

Ignition problems can be tough to identify, but a dyno session detected mine. They use an inductive pickup clamped to an ignition wire for the RPM pickup, and when the ignition breaks up you see it in the data. I't no fun throwing an entire ignition system at your car just to 'check for' ignition problems, but that seems to be the norm due to no easy way to diagnose the opti.

Now if only there were a way to do monitor ignition output while driving, like the dyno operator does......anybody know how to do that? Maybe run a timing light inside the car while driving, and have a passenger watch for the strobe pattern to change? Or an aftermarket tach with ignition trigger from a plug wire? Better yet, borrow an oscilloscope and do the same thing?

 

a friend of mine had the exact same problem, we checked every posible thing, the coil, spark plugs, wires, coil unit, grounds, and we ended up taking out the opti spark and found out that the bolts that hold the rotor were loose, even one was out of its place rumbling around the opti spark, this was a problem on many optisparks, even on mine when I took it out of my car that has 30k miles on it and the little bolts on the rotor were loose. check that. it may be your problem.....