I am 6' 5" and am also a 6 hdcp. I fight the same tendency. My irons are 3ยบ upright and + 1".
I have have been working with my pro (who is also one of my pals), and we finally got in a game simulator and set it on driving range. It was the kind that gives all the feedback: images of your club path, face open, closed or square - stats on swing speed, ball speed, # of degrees inside or outside, # degrees clubface open or closed, impact location on clubface, tempo #s - the works. It was great for my pro because it is hard for these guys to be sure of what the are actually seeing, even with video. The stats were very helpful to him. Also, if you have a non-standard size (tall in particular) it is a little harder to visually read what is really happening in a swing.
It was a great experience, and an extremely productive session. The bottom line for me was that I can come from the inside too much at times. It does make sense after all - if your clubhead is traveling in that direction, it makes sense that it could get too far outside at impact. Now I KNOW what is going on here, and I can confidently adjust when necessary. It makes all the difference in the world. I hope this helps some.
Good Luck.