I wonder what the effect would be, assuming that the result would be something like the sum of both and not a third hybrid effect. I'll write my thoughts, and you can add on or write other views.
Peace+Truth: both make one relaxed and not thinking about what they say. hey'd make the feeling even stronger. And the person would tell the truth, but in happy ways (so maybe that really is an ideal balance ha!).
Peace+Memory: one would end up feeling good but not knowing why. At least they'd feel better about suddenly losing memory.
Peace+Death: again, at least their last moments would be calm; in fact, if Death serum was ever used for humane reasons, for someone who'd die anyways but this would make it easier, adding Peace could help
Peace+Fear: sounds like they'd undo each other and leave one feeling neutral. If fears do appear, they'd just be okay with them and nothing much would happen. If the sim ends when they slow their heartbeats, it'd end immediately. Another mix that isn't so bad for exposure therapy, we could get people to gradually lessen the amount of Peace serum and keep feeling that way with fears themselves.
Peace+Paralytic: at least one wouldn't feel bad about being paralyzed.
Peace+Aptitude Test serum: it could result in Amity choices and give a false result.
Truth+Memory: if memories are really lost, Truth wouldn't be of much use, but if they actually exist somewhere. it could help
Truth+Death: hm, I guess we'd all know how the person feels about dying
Truth+Fear: it could increase fear and make it harder to calm down
Truth+Paralytic: not of much use as one couldn't talk
Truth+Aptitude Test sim: it'd mess with the bus part and make one look Candor
Memory+Death: one would die not knowing anything, but whether that's good depends on what they want
Memory+Fear: they couldn't really be fears if one doesn't remember them, but I'm not sure if sim would end or they'd be stuck, that is, if there need to be fears
Memory+Paralytic: one'd probably be surprised as to why they can't move, or assume they never could lol
Memory+Aptitude Test sim: I suppose reactions wouldn't change, albeit it's a bit tricky for Erudite to rely on knowledge then; ah and the only memory we'd have is the picture in the paper
Death+Fear: it'd be like having a nightmare about dying before we really die in sleep
Death+Paralytic: as shown, they have pretty much the same effect, maybe it's be faster
Death+Aptitude test sim: I guess the sim wouldn't matter, but the test admin would be confused if they didn't know about Death serum
Paralytic+Aptitude test sim: wouldn't change much as people don't move durign the sim anyways