In general, it is good to have your titles running around 60 points if possible. It may also be a good idea to even use bold fonts if possible. Although you might almost never use all bold fonts on a webpage or a printed document, you might consider using ALL bold fonts in presentations. This mostly has to do with the current state of presentation technology and the way that electronic projectors are commonly used in churches. The bottom line is that the projector systems of many churches are still marginal in terms of brightness and contrast.
Bold fonts gives more width and density to letter shapes, thus improving legibility.
This can be particularly important when using PC to TV converters since these devices may drop out portions of letters due to interpolation. Not everyone can see well. This is a particular problem for older folks. Even a lot of younger folks have vision problems that you may not be aware of - and likely, they won t tell you unless you ask them. When I want to emphasize a point then I either use a different color for the font, italicize the text or underline it.