Ignore my previous post. And I had a really snarky “you need to upgrade your internal Believer OS” comment all prepared for you, Als!
Quick test, perhaps it’s invalid but in the past this is how one could easily discern…
Mipmap, .2 filter strength:

Quadratic filter, at 1.0 strength:

Gaussian, at 1.0 strength:

There are no perceivable differences between any of the three. Quick Difference in Photoshop:

Took me a moment to realize there was anything there at all. Quick auto-Contrast:

So only the edge aliasing is affected at all by file-node filtering here, in Maya 2012. I am pretty sure this was working in 2009, but can’t test it currently. I’ll test it on Monday.
I did not alter the edge antialiasing or render settings at all between these three. In the past, Quadratic filtering (default) on the file node would produce a slightly blurry image, thus the need for Mipmap .2 strength. It’s been a preset of mine since 2009, the only preset for file nodes I’ve ever made really.
Nice to know it’s no longer necessary, I guess? (laughs not-bitterly!)