WOT = wide open throttle. (Some guys say WFO. Wide flat out, Wicked ****ing Open, etc)
Plug seems too rich.
Your issue is at near or full throttle, you write
The needle is just for off idle and up to WFO control, but if the jet is too large, too much fuel is blowing in - regardless of the needle setting. Yes even the factory setting is rich, so going with a larger jet will cause WOT bog.
I have a fairly modded engine. I run a .65 main jet, ran great at WOT until I got a slantplug head - now it's too rich again. May go .62...........