This has been my experience with most 3D apps I've used...they all seem to render so slowly at fine AA settings. This method was actually suggested by the makers of my first 3D program as they themselves were unhappy with render times and it didn't[IMHO]seem to impact on quality for some of the I had printed after doing the render large and as bruno suggested, running it through PS to get the correct print size.. ...

 

Once in a while I look around,
I see a sound
and try to write it down
Sometimes they come out very soft
Tinkling light sound
The Sun comes up again