ok, well, T5's have better reflector technology, which makes them more efficient as far as light per watt. With the smaller diameter, you can put more of them closer together, so you can get more light within a given area.
many hobbyists set up two brute containers (with float switches) so that they always have both fresh and mixed saltwater on hand. I keep a small maxijet in each (and of course cover it).
excellent point. This is a situation where the possible downside significantly outweighs the possible upside. The media is relatively inexpensive, so you're better off erring on the side of caution. Great idea about testing it.