The games definitely use 8M save files. They'll work fine at 4M mostly but I've heard some people only had trouble with battle recorder saves on Plat when they're save was too small. If you add the latest savlib file on your flashcard it's meant to make games use correct file sizes if your card doesn't automatically detect the correct size (e.g. my R4 using YSmenu). With that file the saves definitely are created at 8M so... and pokesav only works when the saves are at 8M anyway, or was that just my game
Anyway, I can't get PPSE-DS to work on my 4M saves when using SS, it just corrupts the save file (and I have to delete it using a PC and chkdsk). But it will change what I want on my 8M saves and then shrink it back down to 4M. It's crazy because I then have to use the program to double the size again before I can use the save editor. That's my main problem, which is weird considering that this program was obviously designed for the 4M saves... I'm confused
Note: I have the European version of the game but that doesn't stop this program working on 8M saves. And pokesav works on both US and EU the same except for the AR codes (I need 8M saves for that).
Edit: I don't know why a lapsed into bits here when I used bytes before. Probably because of Pingouin7's post.