At this time of year i've got 100watt infra red bulbs in my royals' 3ft vivs, on dimmer stats. Not ceramic, but I'm assuming the power output's the same.
If in doubt, as long as you use it with a dimmer stat, over-estimate. The stat can always turn the heat down, but if it needs extra power to turn the heat up, if the power's not there, it can't increase the heat. If you see what I mean!
i would say but im rather new to snakes so correct me if im wrong the bigger the better as it will heat up quicker and wont have to work as hard as a smaller bulb and the thermostat will stop the viv getting to hot.