Just bear in mind though, just above the the throttle position where the bog is, there may be a lean spot which will seem to perform well, but will be lean enough to be destructive.
Also it is not only about the revs, it is about the AFR and the position of the throttle.
It possible to have the revs way up, and be feathering the throttle giving a varying mixture, at times which could be lean.
I don't really know if I have explained it well enough, but what I am trying to get at is.
Don't take chances with a poorly jetted carby, fix it or frown.