Here,
https://books.google.com/books?id=M_...actors&f=false
USAAF standard load factor is given as 8.33 g, British as 5.33 g. Not stated if limit or ultimate values.
But here,
https://ww2aircraft.net/forum/thread...uations.23614/
it's given as 8 g limit and 12 g ultimate for US WWII fighters. Values less for a bunt (-g) or as aircraft weight increases (-/+ g). I doubt the Stuka was built to higher values; humans have limits, too.
Highest loads for Stuka would be when pulling and rolling to dive and when pulling out of a dive. Being slow lessens applied loads, which Stuka was.