2014 Mac mini 2.5" SSD upgrade

Question

Hi all.
A long time Mac Mini fan here - after spent almost 3K for Mac Pro (outdated in few years) that I have to "accept" Apple's product refreshing strategies - that upgrade my hardware periodically is the trend.
Since then, I have turned to Mac Mini - for the small fraction of cost, I can "update" my Mini more frequently.
2009 Mac Mini x 2 (mine and my spouse's) are currently at grand children's possession, still going strong.
Now, we have 2010 (TV at bedroom), 2011 (mine) and 2012 Mac Minis.  They were all the top Spec models - at the time.  2012 i7 Quad core, 2011 i7 with 6630M AMD video etc.
Cut into the story - I also put SSDs in all of them ( 1T SSD in 2012, 256Gb x 2 dual drives in 2011 and 256Gb in 2010) plus used Terminal to enable "TRIM" - until 10.10. .. sigh
Along with iOS 8.1.1 - I start to notice the inadequacy of my 2011 Mac Mini - airdrop/hand off will not work natively without some modification.
After tossing around getting an 2012 i7 Quad-core Mini ( 800-1000 USD) or - jumping into the fixed memory, 2014 Mini?
I decided to order a base model of 2.6GHz i5, with stock 1T hard drive, 8G ram (639-699 USD).  Because I have few 512Gb SSD sitting around - I was torn to order the higher end model with PCI-e Apple OEM SSD 512G.  After all the price adding, I realize I can buy TWO base 2.6GHz i5 Mini than 1 customized high end Mini.
Through the web, I found the Fusion drive model (2014, oh, with USD 200 extra) has PCI-e 128Gb SSD and 1T HDD.  I am hoping one day, iFixit will have the part for the PCI-e cable/setting to be placed in 2014 Mini - for some people want to play around.  For now, I am settling with slower speed of SATA-3, third party SSD without TRIM.
According to UPS, the my new toy will be delivered Monday and I will post more details about this SATA SSD upgrade process.

Answer 1

After few days of testing.
I finally solved the problem of screen flickering ( when an app is opened, or few apps are opened), the screen will flicker on the app(s).  This happened on Firefox, MS Word, Soundtrack (yes, I am still using it). iTunes, iPhoto, even "system preferences" etc etc.
First, my system was built via Time Machine restore - after SSD (Crucial 512Gb) on the SATA-3 port. ( theoretically would be slower compared to PCI-e SSD) on my 2014 Mac Mini 2.6Ghz, 8Gb memory. ( I chose the basic 2.6Ghz base model to save few $$, since I have two 512 Gb SSD laying around, instead of custom-build for 512 GB SSD PIC-e, with USD 1,299.00 price tag).
I tried numerous methods to avoid the flickering ie - PRAM reset, HDMI -> monitor, HDMI -> DVI cable, Thunderbolt -> DVI, Thunderbolt -> VGA on two different models of screen : no success.
The only time I could get a normal decent "flicker free" was when I booted into safe mode - after reboot - same issue.
I also used hardware check as Mini indicated "no issues" on the hardware.
I went to Apple Store and play with their set up - no issues (of course, Mac Mini was hooked on the Apple Display, wow!)
I started to wonder - either it would be OS X issues or "third party" software??
So, I took the 512 Gb SSD out (it is some sort of "pain" to open 2014 Mini), then used another SSD (120 Gb) for a clean install.
A fresh 10.10.1 on 2014 Mac Mini without other 3rd party software - worked great, no flickering at all.
I started to add the apps I normally have, one by one to test - UNTIL -- Microsoft Office 2011 (home and business version)
I have Outlook to synch with my Calendar, and typical Word, Excel, Powerpoint on my system.
As soon as I put Office 2011 on it - Voila!  I found the culprit.  It was running 14.4.6 version.
So, I put my 512Gb Crucial SSD back (another pain again) and booted up normally - same issues.
I have been check Apple to see if OS X 10.10.2 becomes general public release (hoping the problem would be accidentally fixed) - in the mean time, I was using my 2011 Mac Mini as the main system.  2014 Mac mini was on the disable list.
Until today, Office 2011 released 14.4.7 - I gave it a try and finally, Mac Mini 2014 with Iris GPU would not demonstrate "flickering" issues after the update!
Whew!! 
Sam