Drumroll, please . . .
My experiment results are as follows:
Started with egg whites from 5 cold eggs. Added 1 1/3 cups extra fine granulated sugar. Mixed with whisk in large Pyrex measuring cup (Maybe 12 or 16 cup capacity).
My microwave is 700 watts, which is pretty weak. I cooked on high at 30 second intervals, stopping to whisk after each interval. After 6 - 30 second intervals, I was near 150 degrees, so I backed off to 10 to 15 second blasts. Got to 160, poured in mixer bowl and whipped. Added 3 sticks butter and switched to paddle on low, along with 2 T. Vanilla.
My result was just under 4 cups buttercream.
My observations: I would start with 60 second intervals next time, do 2 of those, and then work down as I got closer to 160. The resulting meringue was thick, dense and gooey, like a marshmallow creme. My IMBC meringue is very different - very light and airy, and gets even more light and airy (like clouds) when you add the sugar syrup. Is this just how SMBC meringue is, or was that because of my microwaving? I don't know. Maybe those of you who make SMBC can chime in.
Have to run, I'll post more later!