The titles are a little confusing; "Complete", "Ultimate", "Wow, that too!", but its not too hard to get the info that you are asking about.
The IL2 "Complete" has all of the IL2 versions through Pacific Fighters and associated patches, i.e. version 4.04 (merged).
The PE-2 add-on has been available only as a download, so far. The next add-ons, Sturmoviks Over Manchuria & 1946, will also be available as downloads if you want to go that route. These 3 versions are 4.05-6-7, respectively.
Here's the good news! The release date for these next two add-ons is less than a month away AND they will also be available as one DVD with all, repeat ALL, of the IL2 content through 4.07. This DVD will also contain some cool extras like background info on the game, a large pdf on the planes in the game, and more. Check the link on Mission4Today.com:
http://mission4today.com/index.php?name=News&file=article&sid=66
The bad news (at least for those in N America) is there has not been a US/Canada release announced, but the site GoGamer.com will likely be an avenue for snagging the disk once its released. I think the DVD containing the whole shooting match is the best buy but you could still download each of the 3 add-ons (-.05, .06 & .07) if you wanted.
Search this and the M4T forums and you'll find lots of discussion about this.
Later,
MudPuppy