Hummingbirds- How slow do you go?

I've been pushing myself to try lower shutter speeds in natural light while using a Manfrotto 393 head. Its been a pleasant surprise. I've had decent results as slow as 160th of a second but 250th of a second seems to be a sweet spot.
1/250th sec/ f6.3/ ISO 400 (7D with 200mm 2.8L II and 2x extender II)

How slow a shutter do you shoot hummingbirds with?
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Fish are evil