The US release is longer because it is the Director's Cut, while the UK release is only the Theatrical Cut.
Various scenes are extended, plus there is at least one notable scene which is totally new (the death of Hollis Mason)
Also, as Blu-ray Discs are in 1080p, I think that the speed is the same whether in the US or UK, as the whole NTSC vs. PAL thing does not apply.[but even if the 4% difference did apply, it would still be a rather minor factor, given that the difference in run time is due to the different cuts of the movie).