Here's a little chart I've put together regarding M96/M97 engines. They all have a very similar block, except for the 996 GT3:
Be careful comparing factory weight specs. Options can throw things off. Just a guess, but I'd bet that a fully loaded base 00-04 986 manual would weigh about the same as a really low option manual S model.
FWIW, somewhere I read that the 6sp is about 100 lbs heavier than the 5sp.
I don't know the weight of the tiptronic, but it wouldn't surprise me if it weighed the same or more than the 6sp.