Tried it out, the black bars are still there. If I set the output to my HDTV to 1080P I get black bars on both sides of the image, and if I set it to 720P it fills the screen, but I get black bars on the top and bottom on my MacBook. So there's a trade-off. :/
Edit: Never mind, I'm a doofus. This is only when it's set to mirror mode, but since I'll be using the HDTV, it doesn't make a difference if there's black bars on my MacBook when it's outputting 720P. The only problem is still 1080P, which would be nice to have but not necessary. Hope that answers some questions.