I know this is a old thread but it's still helpful. I just wanted to comment that I am using a NGK. in a Zeda with a speed carburetor and a 40 tooth sprocket. I had it gaped at .028. and it ran okay. In a video the guy says .035 on the high end. And in this thread, some commented saying around .030 to .035, some say even more.
So I gaped mine at .035 to see how it would preform. And I'm telling you it really perked this engine up. I had to readjust me throttle setting. Anyway it worked out for me!! In the past this bike had top out at 40 mph. And now I think I can get more.
One other thing, each of us has their own bike style and set up so that's where your judgement and feel come in. Good Luck~