Ok, just took a bunch of series with HDR on. It was auto before. It seems to add just a slight delay before the bursting started.
The landscape still action came out great. Took about 5 bursts. Then I took about 30 of my dog running around the yard barking at the garbage truck. Surprisingly, not a single shot was blurry. I'll mess around more later, but so far the only downside from HDR on rather than auto or off is that there's slightly more delay than normal for the first shot. The normal shutter lag is pretty noticeable though. I'm guessing here, but with HDR off the shutter speed feels like half a second. With it on it feels like just around a second.
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