Just to clarify my own problem, as I orignally said it's only the 2nd and 6th, whether it's with or without capo so I'm confident the Shubb isn't my problem, especially as I always place it close behind the fret and have it fairly lightly tensioned anyway. However (!) I've just been looking at the G7 which is going on my shopping list tomorrow.

Been looking at the action with new interest though, some of you may have a point....