While I'm editing, can anyone offer a general comparison into how long it takes (in manual labor) to bottle 5 gallons via natural carbonation vs. bottling from a keg using a counterpressure setup? From my research, it seems inefficient timewise. I know it's a bit off-topic, but it may aid the OP in deciding whether to convert to kegging?
For me, it's pretty similar. When I'm filling bottles from the keg, I try to get a little foam on the top of the beer, in the neck of the bottle; that displaces oxygen and I put a cap on top immediately. Those caps sit in the vinator, in Star-San.
When I get going, I can fill about two bottles a minute. It's all in avoiding wasted motion. I put a bottle on the vinator, give it a couples squirts of Star-San, pull it off and swish the mouth in the Star-San, then as I hold it in one hand, I grab the next bottle, swish the mouth in Star-San, put it on the vinator, squirt-squirt, then fill the first bottle. When that's done, the bottle on the vinator is done draining, I grab pull it off, grab another, swish the mouth, squirt-squirt, then fill the one in my hand.
I've chilled the bottles so there's not a big temp change as the beer enters the bottle.
When I have about a dozen filled, I cap 'em. The enemy of speed is doing each bottle one at a time from beginning to end. I've found there's a kind of a rhythm to doing this, and the more efficient I can be at each stage, the better.
One more thing: I have filled bottles off my taps using a growler filler--it works well, I can get that little bit of foam on top, and cap 'em. As long as the bottles are chilled, and I can control flow rate (I have flow-control faucets), it's very fast.