Sounds like too much "lag" to be sustained.

The more the shaft stressed (effective weight), the tougher for it to be maintained, due to gravity, the stressed shaft and your subconcious "hacking" intent.

Setup Down the Line
 

Here's a still that i've taken showing how i'm currently setting up.. again looks like right forearm too high at address which may lead to the running out of right arm?

Getting the right forearm more on plane as i mentioned just feels like i'm cramping the ball too much

Setup - 7 Iron & Driver Down the Line

Cheers

Axis tilt
 

Bergsey

It looks from your earlier photos you are not setting up with axis tilt. To set up in the position you want you have to drop your right shoulder when you grip the club. Your upper body will then angle back and your head will set behind the ball. You will be able to to have the bend in your right elbow and you will find your shouler turn will be dramatically easier.

Dave

Setup looks fairly decent, but you want to relax that right arm. Just let the elbow bend and be lower than your left. At impact fix, someone should basically be able to slide a shaft into the gap (under your left elbow, over your right elbow pocket), from down the line. A slight exaggeration, but should get you feeling the right forearm being lower, and will get your axis tilted a bit too. When you are in that position, imagine that you are taking your hands up a plane that is 'between' your arms.

Your left foot looks a touch to square to the line, you might experiment turning that open a touch, which will let your pivot move through better.