I think you have the camera's shutter speed confused with its frame rate:
1/4 - 1/8000 (video, manual control), 30 - 1/4000 (photo, manual control)
25p/50p recording - Shoot smooth, cinematic Full HD video footage with choice of 25p/50p (progressive) frame rates
A camera that shoots 8,000fps would be very rare and ultra expensive.
As a side note, if you did in fact have footage shot at 8,000fps,
you would likely have to specify that frame rate in the Interpret Footage menu for that clip.
My understanding of cameras with overcranking is this - if the camera natively records a video format with 50fps, and you set the "overcrank" to 100fps, the camera WILL record 100fps, but writes them to the video file at 50fps, thereby doubling the playback duration. Playback at the standard frame rate then appears as smooth 50% slow-motion, without you changing the speed in the edit software.
If you use 200fps, playback at the standard 50fps would appear as 25% slow-motion.
The recorded clip properties will not reflect the overcrank frame rate - and 8000 cannot be correct....you don't have a Phantom camera!).
Please review the manual for the camera to gain a better understanding of the capabilities and limitations. I think you may have changed the SHUTTER SPEED and not the frame rate.
Safe Harbor Computers
While many cameras DO offer the ability to "overcrank" for a short duration, such as to capture a golf swing in slow-motion, I looked at the specs for your camera and don't see that feature listed.
Raising the shutter speed means that the shutter is open for a shorter duration during the exposure of each frame of video. At slow shutter speeds, fast motion will look blurred on a freeze frame or during slow playback, because the subject moved quite a bit during the time the shutter was open. A fast shutter will "freeze" each moment in time clearly, but also lowers light sensitivity, so best used outdoors in good light.
It can be fun to play with shutter speeds - on my honeymoon, I was shooting the airplane prop out my window and cranked up the shutter speed until the prop STOPPED and I could read the serial number off of it in my viewfinder!! Note this was in the old days with CCD sensors - the new CMOS sensors have skew which warps the image in many cases.
Note that very high shutter speeds will result in choppy motion, so only use as needed.