>>for more contrast do i shoot tri x 400 at 800 or 50/100?

By now you probably know the answer but if not here it is. You get more contrast by increasing development and less contrast by reducing development i.e. it's the development that controls the contrast, not the film speed. However, to compensate for the increased development (to get the extra contrast) you need to uprate your film to a higher speed (800, for example) otherwise the highlights will be too dense (or 'blown out'). In summary -- increase your film and increase your development to get more contrast. You will, of course, get less shadow detail when you do this and a bit more grain.