I'll admit I don't watch overseas football now, because I don't want to pay more money for access.
I'm sure Perth and Roar fans will disagree, but the AL has improved so much recently in terms of - handling speed of players individually and faster team ball circulation, teams sustaining possession for longer periods, I can't deicide on a best league to go to immediately to play in overseas. Japan, Holland, Switzerland and Belgium are good destinations if good enough and players get minutes.
Going to the UEFA Big Five, or the 30 or so big UEFA clubs in more modest leagues can be too big a step up.
Apart from Miller and Baccus, I believe players stagnate when they go to Scotland. They become better ball winners, but when it comes to first touch, passing and moving in tight spaces, 1v1 dribbling skills, running with the ball, tactical nous, unless they play in the Old Firm , like Rogic and Mooy did, I see little improvement in players playing in Scotland. Popa isn't selecting them like Arnie. Popa is also looking past English League One too.
Re number 8s and 10s - Jake Hollman and Segecic are looking excellent to me in the A L. Jelacic is decent too. The latter could do with playing with a few better players than he currently is.