I have to agree, just keep at it until you get it right, otherwise you'll fall out of this hobby very quickly. You may think the pep stage is difficult, but wait until you see the sanding stage...
I wouldn't recommend Agbates' file until you are comfortable with your pepping skills on things such as FS's HD torso or helmet. Especially with the chest pieces, you're looking at a LOT of time spent cutting, scoring, and gluing, so slow down and make every tab count, and you'll find that you're better at this than you thought.
Since it seems the majority of Mark IV parts are medium-high def pieces, try building Robogenesis' low def Mark VI if you haven't gotten the hang of pepakura. It's not difficult if you take your time, and there really isn't any sort of skill involved, just patience.
Hope you find what you're looking for