But the OP says the difference is between 17 and 19 lbs thrust not 30 and 19. No offense but are you sure you can tell that difference holding it in your hand?

IMHO it is logical that the higher RPM turbine had more thrust, but is that what the complaint is? The complaint appears to be that one turbine is below some low end thrust spec? Or is the complaint that Barry will not raise the RPM?

Also, you appear to be assuming that "old" and "new" turbines with the same name are indeed the same internally. I don't know about Kingtech but I can tell you for 100% certain this is not the case with other brands. Anything can be different internally (or even assembly process, balancing, anything), and in many cases as the turbines get newer the RPM can safely be increased. I want to stress this is not Kingtech I am speaking of.