Wieniawski 2
Vieuxtemps 4 or 5
Arensky Violin Concerto
Bruch Scottish Fantasy
Conus Concerto
I don't know the Arensky well, so I can't really comment. Scottish Fantasy is fun but I wouldn't say that its pedagogically necessary or that valuable. Conus is an interesting piece -- some do it really early in the sequence and it just doesn't seem to work well in my experience. It seems more valuable if done a bit later, even if it supposedly is not that hard.
Is for Vieuxtemps 4 vs. 5, I would say that technically #5 is probably harder (especially the looong cadenza), but I find it musically a bit lacking. It is a great pedagogical piece, though, in that it covers a wide range of skills that will be needed for the really big concertos. #4 is technically a little easier in my opinion, but musically more interesting.
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Vieuxtemps is probably good to study, even though I think all of his music is among the most insipid in the violin repertoire; maybe that's precisely why it should be studied. My teacher had me study V2 a while ago.
I love listening to the Scottish Fantasy but don't know the first thing about its challenges.