My experience in PCs dates back to 1992 (60Mhz Pentium) and before that to 1969 in DEC mainframes with multiple discs running side by side. Data reading and writing on hard drives, although much improved and still improving, has lagged behind the ability of the CPU and Ram memory at all levels of computer technology from the beginning 75 years ago. The best way to improve data throughput has been to duplicate the hardware and have each piece working towards the completion of the task required. Sometimes we used three printers to print a long report. Sometimes we used 4 tape drives to provide the data. With the personal computer whose CPU capability is awesome compared to mainframes (which is why there aren't many of them today) with tremendous memory by comparison (and unfortunately often over-bloated software written in the Charles Dickens style: he was paid by the word) the best way to improve the performance has been to 1) increase the ram memory (subject to M$ limitations) and 2) carry the operating system and frequently used application programs on one FAST hard drive while keeping the files for games, music and video on another reasonably quick hard drive. Better still, partition the storage hard drive so games, video, music, pictures and documents are separated so that files that lend themselves to sustained reading throughput (games, video, music) are not co-mingled with each other or with pictures and documents. The current trend to use the SSD as a fast hard drive for the OS and programs makes a lot of sense. Game files can be read fast when they are not fragmented or mixed with other files. I've had 5 partitions on a storage drive and you know when you've got it right when optimizing a partition results in just a little defragmentation with no rearrangement of files.
My preferred set up today is a quick HDD for storage and an SSD for the OS . Cost of the SSD dictates its size and its size dictates how many program applications you can afford to put on it. But in any event, this is currently the fastest way you can increase your data throughput after you have already increased your ram. I suggest you carry the first partition on the HDD as a copy of your OS and any programs on the SSD so you have a backup in case the SSD gives trouble. I also suggest that you have a backup of the entire storage drive, which is supposed to be a reasonably quick drive such as a WD Blue or Black or WD Re, Seagate Barracuda or SSDHD, an HGST DeskStar or above, Seagate Constellation, Toshiba 4TB or 5TB. The emphasis should be on 3 year or longer warranty, reasonable durability and performance attributes, 64MB cache or larger. The less you shut down your HDD and your PC in general, the longer it is likely to last without trouble unless you have a cooling problem which should be solved, the sooner the better.