That is one way to do it...I like 400x100 sigs, but sometimes they are so busy that I have to make them smaller, such as 320x85...
The other thing you can do is "optimize" them. If you have Photoshop, use the "save for web" tool. Mess with the settings and get the file so that it is under 10240 bytes. Have fun!
The One, the Only, the Incomparable Mercer Boy. My My YouTube.