I am wiring up some RJ45 network sockets for the first time. (MK
Electric part K5845 - available in UK)

If the pins in the front of the socket are numbered 1-8 left to right,
then the corresponding connections on the IDC block on the rear are
arranged as follows:

4 X X 5

6 X X 3

8 X X 1

7 X X 2

Why is this arrangement used?

I can see how the wires in the pair to terminals 7 and 8 are kept
together, as are the pair to 1 and 2.

But you have to untwist the pair going to terminals 6 and 3, as the
wires in this pair are on opposite sides of the block. You also have
to untwist the pair going to 4 and 5.

If keeping the twist right up to the terminal block is important, why
isn't the IDC block arrangement as follows:

4 X X 6

5 X X 3

8 X X 1

7 X X 2

or am I missing something?