It depends on the data. For one app I've written my own CouchDB driver which, as slow as CouchDB is known to be, seems to kill most AR equivalent code. That's pending release as soon as it's stable.
Generally speaking, I think AR's problem isn't really an API one, it's a great interface. It's that it's implementation is far too clever and would benefit quite a bit from narrowing supported driver styles and removal of some old APIs that really hurt more than help. There could also be better control over opt-in on some behaviors that start adding up in overhead (i.e. change tracking keeps a lot of garbage around).
Generally speaking, I think AR's problem isn't really an API one, it's a great interface. It's that it's implementation is far too clever and would benefit quite a bit from narrowing supported driver styles and removal of some old APIs that really hurt more than help. There could also be better control over opt-in on some behaviors that start adding up in overhead (i.e. change tracking keeps a lot of garbage around).