You may already have done this but you can usually download some control software from your motherboard manufacturer's website, once installed you can control your fan curves from Windows instead of from the BIOS allowing you to adjust in real time whilst using the applications your interested in, e.g. 4k video playback.
Regarding the fans spinning up and down, this can sometimes be allot more annoying than the fan noise itself and is typically a sign that your fan curve setup is oversensitive within the temp range your PC likes to operate. There is usually an option in this software to control the sensitivity of the fan speed change, each manufacturer calls it something different, something like interval time, or speed delay. What this option allows you to do is change how fast your fans react to temperature changes which can smooth out speed changes into a more gradual and less noticeable change, more pleasant on the ears!
Regarding temps, 50C - 60C for a medium load task is well within acceptable limits, personally I would be tempted to adjust the fan curve so that medium loads run maybe 5C - 10C warmer, which should help to keep the system silent even during tasks such as 4K playback.
When I set my own systems up for prioritising silence (e.g. HTPC usage) I try to set the fan curves so you can only hear them once the CPU reaches above 70C, which if setup correctly with a good CPU cooler and quality fans should be rarely.
A simple way to do this would be to set 0C to 0% fan speed, then 70C to the just about audible fan speed, which could be for example 50%, then the final point on the fan curve would be 100% speed at the temp you would consider your maximum temp, for example 100% at 85C. If your system cooling is sufficient this style of fan curve will keep your CPU silent under everyday light to medium usage tasks such as media consumption if this is your priority.
If you regularly undertake heavy usage tasks such as gaming/encoding, etc, then the above type of fan curve probably won't be suitable.