If you're going to have the OS and programs installed on it then yes you want a 7200 RPM disk, but for storage then 5400 RPM is fine.
By the way, WD Black drives are always 7200 RPM because they are performance drives, so CrystalDisk is wrong. Only the Green, Red and Purple drives are 5400 RPM.
As others have said what you want is a 250GB or 500GB SSD for Windows and programs and a large capacity HDD for files. 250GB drives are affordable at the moment but in a year 500GB will be. A year ago a 500GB Samsung 850 Evo cost about £130. Now thy're £120 so in a year they'll be about £110 or maybe even £100. 250GB is well under £100.