Cool! the only time i would need it to scroll faster was if it was in front of the map being drawn, which i might want, but that's something that would be a special case and i would add the myself any way.
EDIT:
also i noticed this in the header file,
If SFML has a method of returning image size for a sprite, let me know so I can change it so they don't need to be passed in.
I believe you can get it like this,
sprite.GetImage()->GetWidth();
sprite.GetImage()->GetHeight();
EDIT #2
Ok, I added the multi-speed scroll ability to the DrawMapParallax by adding a nother argument "float scrollSpeed", and if set to 1, it will scroll at the same speed of the map, the closer you get to 1 the slower it is, so 1.7 will scroll faster than 1.2.
works pretty well, if you would like to see the whole thing i could post it, but it really isn't much, the "scrollSpeed" just replaces the hard coded 2 in the function.