Live audio driver buffer I/O size?

In Ableton Live feeding a return track into itself effectively creates a delay line - with size equal to the active audio drivers output buffer size it seems. Using Max for Live, I'd like to use a return track like that as longer delay line but compensate for the inherent latency in a way that takes into account the buffer size of the active audio driver.

Is it possible to get the buffer I/O size of the active Live audio driver from within Max so I won't have to manually input it?

[dspstate~] seemingly always reports a vector size of 64, regardless of driver settings, and to use [adstatus] I would still need to find out which driver Live is currently using. [adstatus latency] always reports 0 in M4L devices as far as I can tell.