Steve,
To show what you are up against in the wide market place the photo at the bottom of the first post in this thread is a fake. There is a huge amount of pictures on the web.
http://www.vintage-radio.net/forum/s...d.php?t=124222
As sugested above I might be inclined to pre test. Get a big heat sink and whilst keeping an eye on the temperature derating and safe operating area push up the current whilst watching the specs for saturation voltage as per the data sheet . ON Semiconductor quotes 1.1 Volts saturation at 400 mA base and Ic at 4Amp and 3.3Volts saturation at 10 Amp with 3.3 Amps base drive. But that is ON Semiconductor specs and I dont know the variation on other "Good" brands. But it should sort out the fakes as I doubt they would meet that test for long.
Pete