I didn't think superhuman was that hard on R3. It was easier than R2's superhuman for me and that didn't seem nearly as hard as I expected. I'll gladly help you with it, it might make it easier on you since we can revive (and also crawl towards health packs if our partner isn't able to get to us right away I found out), but the arena level in PA will be a lot easier for you if you do it solo since its uber tough in co op. They double and maybe even triple the ammount of grims and leeches they throw at you. I did it solo after finishing it co op and was like WOW that was easy!
I will keep an eye on it whilst you are working through it.... Once complete I can make a decision on whether to pick this game up.... I am a certified trophy whore, so my decisions are based on how easy etc.....