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don't know if you're talking about martial arts/boxing shots - in this case I love to drag the shutter (for training shots). A D600 with 24-70 is close to perfect for this kind of stuff.
A Speedlight is a must in my opinion (I'm still using a bgunch of old SB-800's).
Depending on how "dirty" I want the final pictures I gel the flash to match the usual ugly ambient light or not ;-)
Usually I shoot at around f/4, ISO1600 to 3200, shutterspeed around 1/25sec.
D700, ISO1600, 24mm at f/4, cropped a bit, 1/25sec, flash not gelled to match the yellow ambient light
D700, ISO1600, 28/2 Ai at f/4, 1/25sec., no gel on SB800 - PPed to suit a weird taste ;-)
Hope this helps and please excuse my bad English, Georg.