Okay Liz, let me get this straight, some contractors want to apply #4 on top of your driveway.
#4 is a recycled mix I believe, and isn't really a new batch of asphalt, ..but I could be wrong. I don't think you'll get a great lifetime out of a #4 application, and suggest you go with the more expensive options.
I'm not an expert, but I think I've phrased your question a bit for others.
Repost if noone responds today. Not everyone can get to the board everyday.