I think over-springing is the main issue. Don't look at it too hard Gus. You need to use a cam setup that is easily replaced. Even if you do everything right, you will still need a replacement from time to time, so using parts that are easier to get is the way. Just with some decent single springs. With solids, you just don't need to be so over the top with stuff.

Mine revved to 7400rpm with no problems on single springs.