Are you on dial up or measured service?
I am on highspeed cable and a 5 Mb file is basically insignificant.
it all depends on the traffic shaping policies of your ISP, but generally speaking should matter. I would use email if possible. Once it's uploaded, it resides on the mail server... your bandwidth is no longer in the equation.
Thumbs down on yousendit. These are much better and free:
http://www.megaupload.com
http://www.sendspace.com
http://www.rapidshare.com
http://www.filefactory.com
http://www.badongo.com
Oops, I forgot to include zShare in the above list:
http://www.zshare.net/
It's another good one and virtually unknown.
The main difference I can see is if you send via email, the 5 MB counts against total inbox space. That's not a concern with gmail, or another "large" service, but many other commercial accounts only have 5 MB or 10 MB limits. Given a choice, I'd set up an ftp or some other download method. Then again, maybe I'm too old-school (i.e. five years ago) in my thinking...