In my recent experience, pairs are still much in use. It really depends on the ferocity of the shoot. For a big shoot (400+), pairs are an advantage, although not an absolute one. I would suggest that, especially on partridge, you'll get a deeal more shooting with a pair than you would with a single gun even with a highly competent stuffer, but you'll still be able to take your full share either way. On a family shoot, it's rare to use a pair and it might be felt you were trying for an unfair advantage.
As for the differences in height between drives, thats why Nigel Teague is doing so well these days. I know Purdeys will make up a gun already Teague choked and even provide velvet-lined holes in the case for them.
