https://nikonpc.com
The “PhotoIO Cineflat”, “TassinFlat”, and Flaat_12P are probably what you are looking for.
Select the profile, download it, and copy it to the root of your card. Then use the Nikon menu to load a custom profile, choose it your shooting mode.
You can see if https://nikonhacker.com/ has a firmware for your camera, which can give you higher bitrate recording at the cost of less record time.
I find my D5100s seem to be native at about 200ISO, 100 looks to overly contrasted, and 400-640 starts to grain up.
Using a non-kit lens (lens that came with the camera) can give you much more resolution and often time faster stops. A set of 18, 24, 28, 35, 50, 85, 135 F2 primes is what I use. The older manual Nikon lens are sharp and great, much better than the auto focus DX series lens. With manual lens in Manual mode, keep your shutter speed the same as the frame rate, or double. Do not go higher as you will get more strobing on moving objects. Pan slower than you think to avoid the pronounced rolling shutter and AVC motion artifacts.
I still tend to use lens filters like pola and ND grads to help with increasing the stop range.
I also still use an incident meter, because you cannot trust the onboard monitor in certain lighting conditions. You can get histograms by hitting the down arrow in picture review mode. Taking a snap shot, and then checking the histograms is a good way to verify your not over. Make sure your whites on the histogram are peaking above 235, if 255 is the far right side. AVC codec captures best keeping image details/info you want to see within 16 to 235 or sRGB levels.