This is my experience, but as with everything, it's just my opinion.
Owned Sennheiser IE8's. Loved them, lost them.
Replaced them with Monster Coppers, thought I liked the Sennheiser's better because of the bass. I ended up losing them sort of.
I was in a rush for a flight and bought another pair of IE8s, thought I loved them again.
I recently was given both a set of Coppers and Monster Golds. Today actually, so no burn in on them.
I'm in a position to do back to back on the IE8, Gold and Copper. I love the coppers and golds and IE8s in different ways.
For me at least, I think both pairs of Monster's are superior to the IE8s I think you would prefer the Gold's more than the Copper's. I would describe the Gold's a lot like my B&W Nautalis speakers. Very fun, but perhaps too fun for people that want neutral. The Copper's are like my Dyne speakers. To be honest, I think I prefer the Gold's. But it just depends.
My issue with the IE8 is the bass taking away from the mid. A bit sloppy. You get the same punch from the Golds, but without the sloppiness. By all means though, the IE8 is wonderful. I bought 2 pairs, if that gives you an idea.
Ironically, my biggest complaint about the Monster's are the cable they use. The IE8 is just 1st rate in that department. The cable on the Monsters can pop up over my ear. But, this is a small issue considering the sound quality difference.
As a disclaimer, I received these free from Monster. I'm a bit of a fanboy now too. Either way, make sure you get the Monster SuperTips. They make my IE8's sound great and comfortable.