After putting cobalt flats on my L2000 I am strongly inclined to put these on my SB-2. They are almost as bright as rounds.
The SB-2 is brighter than an SB-1 thanks to the bridge pickup, so you can blend in extra brightness and simulate rounds I believe. The SB-1 has a tone knob so you can cut highs. The SB-2 lacking a tone knob makes me feel like taming the highs is more important, as you can always blend in the bridge for more of them.
I have a SB-1 and a SB-2 as well. I'm tempted to keep my SB-1 with rounds as it does almost every tone imaginable with those. From bright slap lines to sit-in-the-mix P all is possible using that tone knob. Those split MFDs are awesome pickups.
Of course, YMMV. Doing it the way you are covers more ground, but your SB-1 and SB-2 don't back each other up tonally as well.
Very good points indeed. That's why its been difficult to decide.