What is the difference between 60Mbps and 100Mbps in 4K video?
Video compression. In this case, 40% of the video data packets are removed/eliminated/discarded (hence the reduction from 100 mbps to 60 mbps). Using either h.264 or h.265 codecs, compressing and decompressing the 4k video won't result in that much video quality degradation - assuming the vieo is viewed on a 50 diagonal in 4k TV (or smaller). Larger than this and you may be able to see some of the artifacts due to the compression. If you were to increase that compression to reduce the video data packet throughput to 40 mbps or so, then expect visual quality to look more like 1080p... and further reduction to about 15 mbps would get you in the realm of standard def (480p). This becomes more apparent when viewing on larger screens.
Higher bitrates mean that movement and light / colour changes can be represented more accurately. Whether or not you'd notice the difference depends on you and your viewing equipment.
Assuming the dpi is a constant 4096 (4k video) the only difference would be the framerate