Have you tried RVM -vs- rbenv? It may not get the best press in the blogs, but it's always provided a consistent workspace across multiple versions of Rubies and Gemsets, in my experience.
I haven't tried RVM but Ben actually uses it so I've mostly heard the good sides!
My relationship with RVM is that it works for me and I haven't ever really considered switching, but almost everyone seems to recommend rbenv, so I don't try to pull people away from that because I don't have a strong opinion one way or another.
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