Blurry logo in Make theme

I’ve been trying to improve the quality of my logo for some time now and cannot get it done. It’s the header logo over here: http://www.kickstartyourdrumming.com

Two questions:

1.) What’s the recommended image size for a logo in Make?

2.) How can I make improve the quality / sharpness?

Many thanks for your help and for Make theme (it’s beautiful and easy to handle – except for this thingy now)!