i use a powersolutions st7.5, and have literally flogged the living crap out of it
in testing, driving it to 8.1 kwatts into a resistive load for hours on end while working
on heat exchangers, running fuel consumptions tests etc.
the head hardly even gets warm to the touch, i can leave my hand on the case for as long as i like.
maybe not the best heads, but mine seems more than adequate.
bob g