How hard is the Sinding Suite?
It's listed between Wieniawski #2 and Mendelssohn on this list: http://music.indiana.edu/precollege/year-round/strings/repertoire.shtml
This is a very useful piece pedagogically speaking. The first movement is a moto perpetuo. 2nd is very lyrical going high on the G string. the 3rd is a good introduction to playing double and triple stops encountered in solo Bach. I think it is a little easier than Bruch G if you are considering all movements of Bruch.