Question is wether the system is really running at 600MHz or just claiming so in the splash screen.

Does typing "cpu" in the shell also report 600MHz ?

AFAIK there is no way to underclock these cards in SW and both my 2x1800 and 1x1800 (both Sonnet) were reported as 1800MHz way back when I had them in regular use.

[ Edited by Kronos 07.05.2016 - 20:53 ]