Metal seems to me to be one of the hardest genres to do justice with cheaper IEMs, generally because you need something that is bassy so that you can get all the drumming detail, yet not so bassy that they just become mushy. At the same time they need extended treble response as well, since otherwise it ends up sounding blunted. Last of all they need speed, so that fast layered passages don't break up or get dull.
So in fact, what you want is balance and accuracy, which is pretty much what people pay a lot for (and don't always get) even in the most expensive IEMs. Just going by jokers reviews, considering that he has heard pretty much all the options at the price point, the PL50 and the R03 seem like the best options in their price point.
If the PR1 Pro's were still in production, I would have whole heartedly recommended them - I got them for a metal-fan friend in a similar position. Considering that Joker considers the R03/R02 to be worthy successors to the PR1's bang for buck ratio, and that the Pl50 is a relatively old design in comparison, the R03's would be my pick.