I really hate to burst your bubble, but today's gas does not give accurate plug reads. It will show if it is sloppy rich and black and sooty, but otherwise not really at all. The best way of all is a wideband o2 sensor in the pipe. In lieu of that, start with a running combination that someone else has tried and fine tune from there if needed.
I have tried nealy every jet, slide, emulsion tube, carb synch combo I could dream of over the years. I have finally achieved a point where I think it is as good as I can get with limited parts. I find now that if I change something today, like needle clip position, I generally change it back tomorrow. That is a good sign that I am very close.
I did it all with the butt dyno method over several years, I would go months at a time with no change because it was really quit rideable but..... I guess I just can't leave well enough alone if I think I can get better.