in my experience, foam is harder to build with than a pep is, having to figure out the angle cuts and factoring in the thickness...
Having to restart on a pep is pretty common plus since you've already figured out some potential problems the next one should be pretty easy to make right.
I guess what im saying is since you're familiar already with the shape of the mk V and I assume its the helmet you're most attracted to, you could just try again?