I had one bike I thought was broken when it got some cheap supermarket petrol. I almost took it in as it was running so badly. Sure enough after I'd run the tank almost down and refilled, it started to perk up.
My CBR 125 was definitely more economical all year round on super. Even with the extra range it was still slightly more expensive but the convenience more than made up for it. This was the highest revving bike I've had and in theory higher octane is better in higher revving bikes due to fast evaporation or something.
Bigger bikes I've noticed little difference until now but as I say this could be due to the much warmer weather and the resulting effect on oils. Even the grease in the wheel bearings is going to be thinner so everything will move better, not just the engine.
I'm going to continue putting it in as it's only an extra 50p-£1 per fill up and I'll see how it goes. I ran for a long time on normal stuff so I know roughly what that does to a tank.
As for running - it has cut out once or twice on this stuff which it hasn't done since winter but this has only been whilst cold on the cooler mornings and might be just that I've forgotten I need to keep the revs up when it's cooler. I've noticed no difference in power or smoothness.
The biggest difference really is the additives they put in which should in theory keep things cleaner and reduce clogging of injectors, etc. Of course if there's shit in your fuel tank or in their underground tank that makes it through the filters then it probably doesn't matter.
The claim from the nitro+ stuff is that is has more KY jelly in it... I mean lubricants. That's how I read it anyway. They just kept repeating the same damn point again and again as basically, it's the same as the last stuff.