WOW! He is so stunning <3
To me his neck looks a good length, the lower length of the neck is rightly around half of the upper, and not too thin!
His topline looks good as well, and his croup does not lay too low which is good as well. But could be a little more rounded:)
Like lil ruffian said, I deffinately do see the uprightness in his shoulder, which wont cause any problems it is just a slight flaw!
I do see a little bit of sickle hock in him though, which you asked about
Personally I think he could do barrels for a while! Maybe not a decade haha, but a good enough time:)
How old is he and what breed is he if I may ask??