The other references I think are useful are the Ensign 6 O to Z class destroyers book (though mainly covers the O's, less on the P's), and the profile morskie book for HMS Onslow which would be similar to Pakenham (shapes of deckhouses etc.)
There is a discussion on the sinking of Pakenham here
http://www.worldnavalships.com/forums/showthread.php?t=2456&highlight=HMS+Pakenham- with an excellent photo of pathfinder which would be useful for model building. You need to register to see the images. This actually mentions Bernard Lunnon so you may have seen it/contributed to it already!
Very difficult to comment on the camouflage colours - the multi- coloured profile looks like a one off design ? - though there are experts out there! One of the photos on google search shows dark hull/light upperworks which would probably be the mediterranean grey and home fleet grey, or variants of, depending on the year the photo was taken (several of the O's eg. Oribi and Onslow were painted in this from 1941-42).
The plans I have from Deans/Profile Morskie are OK but I'm stuck on some of the details not shown - in particular the positioning of the propeller shafts/A frames which are not shown in cross section on any plans I have seen. I was thinking I might need to order copies of the plans from the Maritime museum in Greenwich but this is expensive so quite a commitment!