The 3:2 macro will self-adjust to a 1:1 rotation when you're under enough haste.
However, depending on your latency, if your autoshot speed is between 1.7 and 1.9, you're too slow for a good 1:1 and too fast for a 3:2. So you either want to get under 1.7 for a 1:1 or stay above 1.9 to keep a 3:2. I'm not entirely sure what the 3:2 macro would do in between those speeds, I just know that mathematically, those are about the speeds that each rotation is perfect.
Maybe I'll go out to Dr. Boom to see what happens. I can get 1.8 speed with some haste gear and drums.
There's a haste/shot rotation spreadsheet floating around Elitist Jerks somewhere that can tell you your weapon speed, and has a chart for steady/auto ratios at that speed.