I can't see any performance hit using iOS 8.2 on iPad 4.
On iPad 2 is barely acceptable, but on the iPad 4 it's fast.
I think 8.2 on the Ipad 2 is totally acceptable; at least to me. I think it is more what people are willing to accept, than a failing per say of the software. For example, many found 6.1.6 intolerable on the 3GS, I did not and I'm still using it.