Best upgrade path for my storage and speed needs?

[LongbowX404]

Hey LTT, been a minute!

Haven't been on here in a while, been out and about with life. <----(super boring, dont try)

So heres whats going on!
Currently in my computer I have a 1TB Samsung 850 Pro that, looking back on it, I spent way too much money on. It has about 50GB free and thats after I went through and deleted the games I am no longer playing. 
I am as of right now, saving up as much money as I can to buy a new Jeep at the end of the year. So I don't want to spend a fortune on my computer currently. It was suggested to me at work (Micro Center) that I put a 960 Evo M.2 in as my boot drive and then use my 850 Pro solely for game storage. I like this idea because of the speed, however for the price of the 500GB 960 Evo, I could be purchasing a 4TB WD Black or similar drive. The speed on the M.2 is fast yeah but currently with rapid mode enabled on my 850 Pro I am getting as follows:

Sequential Read/Write (MB/s)
4,471/4,319 
Random Read/Write (IOPS)
163,394/115,322

I love the speed. It's what I built this machine around. SO all of this being said, can anyone suggest any ideas? I will have an open m.2 slot, 2 HDD bays, and 1 more SSD slot after I move to the new case tomorrow night (Phanteks Enthoo Evolv ATX)

Any advice is much appreciated!!

[Electronics Wizardy]

rapid mode isn't the real speed, its just a very risky cache, id leave if off. a 960 is much faster.

[Energycore]

Don't get such a big drive as boot drive, buy a 250GB SSD (if you want NVMe, the MyDigitalSSD is actually quite good and cheap), and you'll save buck like that while still having SSD performance. If you feel like you need more storage, just a good ole 2TB Hard Drive of any kind, you can put the games you're not currently playing there and move them around into the 850 Pro when you play them again.