That Christmas one is DEFINITELY the Yank so don't get that one.
ChiliD's got 'em all listed well there though like Chili says, most of the comps are redundant if you get the regular albums but you WILL need the ones called "Blue guitar" & "Legend" as they have some tracks unavailable elsewhere on them.
The "2 Greens make a blues" deal is a repackage (with bonus tracks) of an album PG played on by a band called The Enemy Within (obviously to play up the fact that PG played on it to get sales since they must not have been able to think of another way of promoting it on it's own merits.
).
You should also consider getting the V/A comp CD called "Twang! A tribute to Hank Marvin & The Shadows" as Greeny does a great job with "Midnight" (unavailable elsewhere) and the V/A "Knights of the blues table" (which has a different version of "Travelling riverside blues" to other PGSG versions and you can't get this one elsewhere either). Also, there is the 2002 V/A CD "From Clarksdale to heaven: Remembering John Lee Hooker" where the PGSG do "Crawlin' king snake" (not available elsewhere).
Oh, and you may want to think about tracking down the Japanese imports for the first PGSG album and the one called "Destiny road" as they contain tracks not on the other versions of these releases (but do avoid the Japan copies of "Hotfoot powder". You will see ads claiming it has "extra/bonus tracks", which it does, but the "bonus" tracks are taken from the "Soho sessions" live CD which you would need to get for completeness anyways so the "regular" HP will do you nicely).
While you're at it, you may as well pre order the new PGSG album due for release on 24 Feb (in the UK) called "Reaching the cold 100". That same day (in the UK) the V/A tribute to George Harrison will be released called "Songs from the material world" on which PG will apparently be doing a song so you might want to consider that as a pre order possibility as well.
Not sure how far you want to go with this but you may want to try and track down the 2 vinyl Reprise singles from 1972 "Heavy heart" b/w "No way out" & "Beasts of burden" b/w "Uganda woman" billed as being by PG and PG & Nigel Watson (respectively) but before I go in to anymore tangents about other items (as it is, I still have to find an original of the PG/NW one myself)...
Who knows, maybe you will be "a fan of his music" after hearing this stuff of Pete's?!
Hopefully these notes will make it easier for you to get things as complete as possible on that side of your Mac collection though anyways.
John