Great comparison shots, Wor-Gar.
Amazing how bad the ESB sculpt looks in comparison. His whole face is drooping to the front, creating a weird devastated expression.
The ROTJ definitely looks like HT's best Vader sculpt to date. The biggest point of improvement IMO is the inside of the mouth, the teeth and grill. There's a complete lack of depth, making it catch much more light than it should.
For the cape, since it's so integral for his silhouette, I definitely recommend the custom route. But the penny trick looks like a good quick fix.
Looking forward to your final setup/images.