The A3630 get`s it`s clock from the mobo, the crystalsocket on it is for the FPU. You could overclock the whole machine by replaceing the 25MHz crystal on the A4000 board by an 33 MHz one. Could lead to problems with older zorrocards, but in general it works.
For some real speedinprovements while holding compatibility better go for a Blizzard 4030, it runs at 50MHz by default.
