I think being wire wound they may add a little reactance (In the form of Inductance) to the circuit but in the long run, does it matter? I had thought about building my own but if nobody can agree on what the best way to test them, Screw it.... I was going to use these as a base to start with. They aint cheap but neither is a Load bank.
Glen, maybe we should just plug in the preamp and pick a song and test with that. We could start a trend with say... Dokken "Into the Fire", and get everybody to use that for testing the output of an amp. That way we are all using the same thing.