you probably already read this, but if you haven't Tweakers page: Disk Setup
you drive setup looks fine, you can use windows resource monitor to help identify if any drives are struggling as well.
if i were to change something, i would try 2x2tb raid 0 (disk 2 and 3) for media/assets/projects using mbd raid (if your mbd supports raid). i might even try adding the spare 2tb hdd, for 3x2tb raid 0 for even more performance. if "mydocuments" is just random storage (not for your active video projects), you could move that to another drive off the raid, like disk 4 or another spare. since you already have those parts, raid may be a good way to boost performance for free. any raid can add some more risk to data loss, so you would just need to make sure your backups stay current. you can save a copy of the premiere project (just the .prproj file) to a few separate locations at the end of your editing sessions, and/or use auto-saves to another location, to avoid needing to backup as much.
beyond that a single fast sata ssd is comparable to 3 hdd's in raid, so you could look at sata ssd(s) for a cheaper and simpler improvement vs an expensive hardware raid card. sata ssd prices keep falling and show no sign of slowing, so if/when you do get some later, they could be even more affordable.
Do you have a PCIe Gen 3 x4 slot available?
If it is get modern and get one of the new (ten times faster than hard disk drives) 2000/1500 MB/sec Samsung 950 Pro SSD's and an Adapter card. Put all your Project files, media, preview files on this and when a project is finished archive it to those old slow hard disk drives. I just saw today that MicroCenter has the 512GB on sale for less than $300 and for this special price you do not have go to the store!
I know of three M.2 PCIe Gen 3 x4 cards that I have tested and work well.
ASUS Hyper M.2 X4 (not easily available)
Ah ok, that makes sense..im gonna set up that raid then with the extra disk. Performance wise.. where will i notice this performance boost... in general ? or more when editting and exporting and stuff?
thanks for your help!