Does anyone have any information on what is the maximum speed for the gold ceramic z80 CTC?
Since it's labeled Z80-CTC, it's a 2.5 MHz type (Z80A-CTC would be 4 MHz).
Gold or not gold cap doesn't make any difference.
Without a further marking its temperature range is 0-70°C. Wider temperature ranges where are avalable in ceramic but marked CE (Extended) and CM (Military).
(Information taken from a Feb 1980 product sheet)