What's the best size for a banner with the default template?

[K.Ermit]

I'm trying to design a banner for the default theme, but I'm not sure what the correct resolution / size should be.

[Graham Quince]

Because Frog resizes and respostions the background images based on screen size, I've found it's best to aim for 2000 x 250 pixels.  I've noticed our design team tend to use 2000 x 350 pixels.  Here are a few of the banners from Frog Templates, if this helps: