Natural light I'm finding technically relatively easy but you need, in the UK, to push the ISO. At 1600 the 50D is fine. Above this and it gets noisy. The newer Nikons and Sonys have ridiculous ISO but they're bloody expensive. I've managed to get the DSLR housing, strobes, body and lens for about a grand. And if it floods I won't overly cry. Bloody strobes are a ball ache. Still. Seems to be working. Mind you 30m viz helps...
Natural light, ISO 1600
A very fat man being a bell end