Adobe Premiere Pro / After Effects Hard Drive Scratch Disk and Cache set up in temporary situation. I've exhausted all options before asking for opinions in trying to figure this out, and I'm running out of time by doing all possible combinations and running benchmarks, or setting up projects to see which hard drive set up is working best as I have a job that needs to finished today, with what I have available. 

So my usual hard drive set up for Premiere Pro and After Effects is not possible right now, as my main SSD is not working, so I'm left with the hard drives I have left to try and put together a system that will get me through the day as pain free as possible. 

I'm making a short introduction to an interview using Premiere Pro and After Effects (not necessarily at the same time for this project), and working with Raw footage converted to ProRes proxies to save me some precious space and speed while editing. I'm running on Mac (El Capitan) and using CC 2015 if that matters to anyone.

Currently for available hard drives at my disposal I have-


My internal 2 TB SSD. (System drive for OS, programs, etc.)
A RAID 0 configured set of 7200 RPM 1 TB (combined size) Seagate's connected through USB 3. I'm getting speed test results of around 147MB/s Write and 148MB/s Read. 
A cheap 1TB Western Digital My Passport through USB 3 that is getting speed test results of around 60MB/s Write and 75MB/s Read, although I've seen the write speed jump all the way up to 75, and all the way down to 35, so I've never sure. 


So thats what I'm working with for at least the rest of the day. How would you configure your Scratch Disks in this situation? 

I was thinking having my Project files on the RAID 0 HD, along with the Source Video, while the Cache ran off the internal SSD. That leaves the Video and Audio previews. Will the My Passport be fast enough to handle them or should I use either the internal or RAID 0 for them as well? 

Should I move the cache to the RAID 0 and have the Source Video files and Previews run off of the Internal SSD? 

I can't decide so some input would be amazing. Basically the question is, what needs the most and least speed- the Cache, the Previews, or the Source Video files? 

Thanks for your help!
-P.J.
Personally, I would ditch the usb3 drive for editing. Assuming you can't buy a third drive I would do your setup like this. 

Do a two drive setup.
C: OS and media cache
d: (raid) Media, projects, previews and exports.

I've always followed the advice here and its worked great for me.

https://forums.adobe.com/servlet/JiveServlet/showImage/2-2906955-31395/Guideline+Disks.jpg