I have both grades and I suppose I should get around to evaluating their relative merits but the one thing that is immediately apparent from looking at the packaging is that the 300 mesh has a lower resistivity than the 150 mesh - quantified somewhat hideously as 0.37 ohms
per foot (goddamnit!!) for the 300 versus 0.9 ohms/ft (*Gak! Spit!*) for the 150. Divide by 0.3048 to get the more sensible ohms/m value.
Higher resistivity means the mesh gets hotter for a given current, I would surmise(?)
Hope this helps.
“There is a way of manipulating matter and energy so as to produce what modern scientists call 'a field of force'. The field acts on the observer and puts him in a privileged position vis-à-vis the universe. From this position he has access to the realities which are ordinarily hidden from us by time and space, matter and energy. This is what we call the Great Work."
― Jacques Bergier, quoting Fulcanelli