Maybe a tad longer loading times with a 5400RPM drive, but nothing dramatic. 4k video without an issue, yes.
Consider WD Red, they are a bit more expensive than the Greens, but have longer warranty.
I thought the red drives where for raid? I thought the green was as quiet as WD makes?
Both Green and Red are 5400RPM hard drives so they will be about equally quiet as long as you're comparing hard drives with the same number of platters. The only difference between Green and Red is slightly longer warranty on Red and firmware optimizations on Red making it more suitable for hardware RAID.
In general hard drive quietness (if there is such a word) is primarily a function of 1) how it's mounted, 2) hard drive RPM, and 3) the number of platters. Everything else is secondary. Hard mounted hard drives will always be lounder than soft mounted ones because hard drive vibrations will be amplified by the case. A 7200RPM hard drive is always going to be louder than 5400RPM. A drive with 4 platters is going to be louder than the a similar drive with only one platter.
The easiest and cheapest thing you can do to reduce the noise is to decouple your hard drives from your case. I you cannot do that then the next best thing you can do is to swap your two hard drives for a single high capacity 5400/5900RPM drive such as WD Red/Green or Seagate ST4000DM000. A 5400/5900 drive is going to be plenty fast for everything you do and it's going to be significantly quiter. I would probably recommend getting two hard drives though and keep one in an external case for backups.