Job done! Only took about three times longer than expected, so situation normal. Using the vac, the dust was not so bad, but some dust did make it into the garage. At the end I swept up as much as I practically could and then fired up our backpack blower to make the rest magically disappear into the air that our neighbors will be breathing tonight.

Now, using a wire cup similar to this one:
5 in. Knotted Wire Cup Brush | Princess Auto
I'd like to scrub down the portion of floor that I'm going to paint.

Because the max rpm for the brush is 6500, for this job I'll probably use the Hitachi at 3400 rpm. This is where a variable speed grinder would be idea.

The more I use a grinder the more I think back to jobs I've done in the past using a hack saw and file. Yikes! Those would have been so much easier with a grinder.