I no longer have the Mahler box, as I gave it to a fellow co-worker. While I did have it, it didn't sound particularly different or better to my ears. There's no indication on the box that it was remastered in any way. It's only natural that the London critics are going to tout these boxes - they're fighting for the very survival of EMI Classics. But as for Rattle's Sibelius cycle, the English critics are completely out of their minds, as there are many, many far better complete cycles. But given how generally disappointing Colin Davis' LSO Sibelius cycle was, I guess I can't blame them too much. I thought that Rattle's Birmingham remake of Sibelius 5 was positively atrocious, and that his earlier Philharmonia one was far, far better. None of them are top drawer in my book. The decision not to include the recent Berlin remake of M9 strikes me as completely bizarre, especially given just how uncompetitive the Vienna one is.
Barry