In My 4.3.1 Designs I have redone speed bar and used 2 images and changed the css that controls the speed bar to include a <span> Tag, example in images shows off this.
My images are done in adobe photo-shop, and cut to two images to use the proper rollover effect, you could add icons to those, but this is complex.
You could add images but this would require quite a lot of css coding.
SPEEDBAR EXAMPLE:
http://forum.x-cart.com/attachment.php?attachmentid=1862&stc=1&d=126645392 4
IMAGES USED CUT IN 2:
http://forum.x-cart.com/attachment.php?attachmentid=1863&stc=1&d=126645399 7
Hope this gives some inspiration