I have owned a set of Hifi 2009 (not comp) and kite now with Hifi 2011.
The 2011 are not quite as stable as the 2009 hanging over your head. When sailing it is rock stable. It feel to have the same amount of grunt. It has better lowend though while it flies quite a bit faster.
I like these 2011 a lot! They fell like having overall more performance than the 2009.
I have not flied other versions.
The only cavanat: For me 115kg (260lb) I have to pump them very hard in order to prevent them for bending in the tips when loading it hard.
Regarding naming: I think it is just naming. Nirvana was the Hifi 2012