Caddy with HDD + SSD - That’s the sweet spot !. I can totally vouch for the above performance improvement. Did the same experiment a few months, and boy am I surprised.

So I use SSD for running Ubuntu, Android Studio. 
The HDD has Windows 10 in it, and that’s pretty much like the dumping area of large volume data (movies etc).

Also, regarding the SSD model, Samsung Evo and Linux don’t go well each other 
https://github.com/torvalds/linux/commit/9a9324d3969678d44b330e1230ad2c8ae67acf81

Hence I had to cancel my order (Yes Evo was my first preference too) and ordered a Transcend 128GB SSD.

So far things are going pretty good.