Performance difference bewteen AF or AF-S on D750?

[Joe_Photo]

In the context of what the average photographer will experience, what are the performance differences between comparable AF and AF-S lenses?

Bottom line up front:
I made the decision to go FX with a D750. That was the easy part. Now I need to figure out lenses. Specifically I need help confirming if AF lenses are a good fit.

Background:
I'm making the jump from Canon to Nikon and DX to FX with the D750. I do a lot of shooting for dog rescues. Some are more structured pet portrait shoots but what really grabs attention and what I enjoy more are action photos and candid shots outdoors. I find I need to do capture a lot of motion in low light; most of the time without flash or artificial light. The D750 seems a great fit with the auto-focus system and high ISO support.

I’m not brand specific – quality of images is most important. I anticipate my mix being a 20 or 24 f/2.8; 50 f/2.8; and an 85 f1/8 for deliberate shooting. For adhoc or vacation/travel/candid shooting I’m looking at a 35 f/2; and/or a fixed aperture zoom – like a 24-85, 24-120, or thereabouts.

All appearances suggest I can save quite a bit of money if I get AF vice AF-S lenses; particularly if I can find them used. Is there something I am not considering? Does the lens focus motor work faster or better than the camera body motor?

I understand lens motors are quieter than body motors but that's not a big deal to me. AF-S offers the M/A mode. That sounds handy but I don’t have that now so not sure I care about not getting that capability.

Thanks for your help,
Joe