Finger orientation

Hi all! I am not sure if this is already been discussed here... Anyway Thomas Mark (author of "What Every Pianist Needs to Know About the Body) says we must seek for 5th finger orientation instead of thumb orientation. Of course he does not say we can't ever use thumb orientation but as a chronic position it can be harmful. I've been taking this quite seriously recently and I think with 5th finger orientation you don't only get more healthier basic position of the hand, but also more powerful 5th finger. This way it's much more easier to raise its knuckle and make 5th really stand like other fingers. On the other hand it seems to me, that when seeking for 5th orientation it's easy to get some "arm out" movement (moving your elbows little bit away from your center). Is this a down side? Something to avoid or to differently? Any comments on this 5th finger vs. thumb orientation? There's perhaps something between: 3rd finger orientation which means that hand is making straight line from arm to 3rd finger. As piano player and teacher I am still thinking what might be the best way to introduce this to students - kind of a basic position.