I have several of Griff's solo courses, my experience so far was that bgu solo#3 was the hardest for me. Bgu solo#4 was difficult for me too. They were all really challenging at the time, but these two especially almost made me put bgu aside because i just couldn't play them without sounding horrible.
I haven't tried sws yet, but judging by the recordings posted here around solo 4 people seem to either lose interest or not think the payoff is worth the time it would take to learn and record solos 5 onward.
This is a good question, might draw some activity back to the SWS virtual classroom.