I've tried both the Islay and Highland versions in pubs on several occassions over the past year and have a bottle of each open at home (with back ups). IMO they are the best value or 'bang-for-your-buck' malts I've tried at around £25 each for some lovely cask strength 8 year olds.
They are 'mystery' malts but I'm pretty sure the Islay expression is an 8yo Lagavulin, as Macleods seem to have a supply deal with Diageo. The exact ABV fluctuates with each bottling slightly so are very much 'As we get it' from what I can see. I can see the Islay perhaps being Caol Ila from time to time but I'm 95% plus positive the ones I've had are Lagavulin (confirmed by a couple of highly respected stockists).
The Highland I have heard is Macallan but I think this it is more likely to be Glengoyne for recent bottlings, given Macleods own the distillery. I'm open to suggestions on this one.
From what I can see this stuff only gets bottled once or twice a year and is in short supply - if you see it snap it up! As soon as RMW get supply in it vanishes.
The Highland version is an 8Y old Macallan. Its a fantastic whisky for that price and age. When I go for a cigar/whisky combo on a rare occasion (I quit smoking but these combinations are just too tempting) this is my choice actually.
I had not heard of a new release like C.I. implies, but it would be logical. I seriously doubt however it would be Glenfarclas as they have been very strict lately against independent bottlings of their whisky.