Is this the way to get shortest latency in Logic?:
Set Logic to 32 buffersize.
Load MG3 on audiotrack with software instrument loaded in MG3.
Arm track and play.
Or is it faster to use MG3 as a stand alone application outside of Logic and send midi into it?
Thanks!
There is no quick answer! 
TLDR: Use 64 or 128 buffersize. There is a law of diminishing returns as you go lower. Whether you use Logic with the MG AU or Logic with the MG standalone, chances are you will perceive the same latency with sufficient small buffersizes, using the same interface. For DAWs using VSTs you get better latency using the MG VST.
But different audio interfaces have different latency-multipliers too, and you cant believe what DAWs report . It’s difficult to measure. Julian Krause make some measurements of round trip latency in his interface reviews.
32 samples @ 44Khz is ~0.6ms, and even if the audio interface 4x that, its way below your sensory system. But what should the DAW do if you run 100 tracks and plugins and it cant finish processing the buffer in 0.6ms? It can enforce your latency constraint, interrupt the sound (pop/crackle) and cause hearing damage to everyone who were unlucky to be around or double latency internally (and not tell you anything about it and it could double as many times as needed) and go on with higher latency. Logic has some settings related to this (im not sure what they do exactly).
Further there is the multithreading setting, both in some DAWs and a setting in MG which also cause latency. This complicates things further. The next MG update (3.0.51) will simplify this, by automatically control threading to minimise the overhead.
Excellent latency free answer! What if Logic is set to 32 buffersize and MG3 standalone to 64?
Thats probably not an issue. But if you use MG standalone with a DAW, you may want to use two different interfaces, or at least make sure the two apps runs at the same samplerate.
I tried 2 interfaces and MG3 in standalone…seems to work just as well when everything is on 1 interface on my mac mini m2.