Just curious as to what your settings are in the gymnastic shots. I've just just start fiddling around with indoor basketball and with 1/800 2.8 ISO 3200 my images are no where near that crisp? Where they processed in LR? If so what luminance settings?
Sounds like your camera. Tell you what, I'll trade you my D600 for your D750
They installed a ton of new trusses below the ceiling (so that they can support real concert rigging requirements now), along with some strange new lighting. Because of the new lighting, this was the first time I shot at a fixed ISO1600 for over 90% of my shots instead of auto. Shutter is set to 1/1250th. I do run them all through lightroom, but I don't know all the settings off the top of my head. I do know that I don't touch luminance at all, but am not sure if it pops in a default value (like some of the fields) or not. I gave up messing around with noise reduction unless I have a photo that is uncropped & really needs it. Shrinking them down for Flickr gets rid of virtually all the visible noise. Even when viewing the originals at full size (shrunk to fit the display) on my 1920 x 1200 monitors, the noise is not bad at all.
Shooting at 1/800th, do you really need to push it to ISO3200? Also, the reason I shoot at 1/1250th is because that is the minimum speed which allows me to catch action blur-free for the most part. I would think that basketball would require a faster shutter speed than 1/800th. That may explain why some of your images are not "crisp." The hardest part for me was getting the white balance right, especially with the old lights they used. Now it's pretty easy, except that there are a ton of shadows because the only lights in the arena that are on during meets are directly above the floor only.