Got Cubasis running on both an old iPad 2 and a mini retina. Running flawlessly on both (using a bunch of synths, iapp fx, guitar into amplitupe, audiobus, sampletank etc). I guess I can press the mini a bit further than the '2, but haven’t really experienced any problems. Only thing: I regret not having bought a 32 GB mini (only bought the 16GB), as you tend to get “gearlust” (the prices for really good apps are so incredibly low, that you simply can’t hold back) and almost get filled up. However, from a reasonable point of view, I got room for what I need, even on the mini.
