bof wrote:

Is there a spec that says CW1308 must be twisted?

Yes, CW 1308 _is_ the BT specification.

Go to the RS web site (http://rswww.com) and do a simple search for
"cw1308", which will bring up a list of all the '1308 cables they sell.
Click on the PDF icon against any product and you can download a copy
of the actual BT spec. - CW 1308 Issue 8. Note the requirements for lay
length (section 4.2) and reference to twists in section 5.

--
Andy