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<p>The D750 is upgraded to the high-end AF module but the shutter remains to be the one rated to 150K actuations, similar to the D600, D610, and Df. Personally, 1/4000 sec is fine; I rarely use 1/8000.</p>
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<p>I own a D7100 and a D700. I have been interested in seeing the 24mp FX sensor in a higher spec body for some time. I don't use 1/8000 much either, but I do use 1/5000, 1/6400 quite often. ;)</p>
<p>That being said, I don't really mind the 1/4000 limitation, but feel a bit odd spending $1000 more for a body that has features I would consider a down-grade from my D7100. I may not be the target customer for this body, but some of the choices Nikon made are confusing to me none the less.</p>
<p>This is the reason for my speculation on Nikon needing another use for the 1/4000 shutter. It makes no sense to me to have crippled this on the D750 body. I can't speak for everyone, but it's giving me pause and perhaps a reason to wait before upgrading.</p>