Thanks mate. I just wanted the info to appear here from a credible source (being yourself) because I've had discussions with quite a few folks who think that an M.2 SSD is faster than a SATA SSD. Having bought one are then surprised to find no real performance improvement. I know the facts of it but lack the certainty of some of the things I think I know.

Just to clarify the M.2 SSD in my new Dell Laptop is a Sandisk X400 M2 2280.  
As it is new, I haven't opened it to see if the cabling (SATA and power) and holder is there for a hard drive (or full size SSD).  But, according to one of the "experts" on the Dell Community Forums there is a very good chance the hardware is not there since the M.2 SSD is "standard" in this particular model.

Jim Roseberry

soens
SSDs and M2s are super quiet and fast over SATA drives. Today's laptops are probably the most noise cancelled systems you can use as towers still need hefty fans for big CPUs. I use M2s for boot drive, sample libraries and main file storage. SATA for DAW projects.

Disagree with laptops being lowest noise.

Far be-it for me to disagree with your disagreement Jim, but... I did say "probably". There is far more control over tower builds than laptop choices. But my i7 laptop is, for the most part, completely noise free. Running 2 M2 SSDs and only occasionally do my failing ears hear the fans. They're whisper quiet. If left on and working the CPU they'll kick in louder but only for a few seconds. And it has more than enough power to run Sonar for my needs. For the price I don't think it could be beat. (It was on sale tho)

Update on my post about my new Dell Laptop.  I bought a Samsung 500GB M.2 2280 SSD for it.  Opened it and replaced the original 250GB SSD.  I had a Macrium Reflect full disc backup and restoring to the new one went with out a hitch.  After it was up running, I downloaded "Mini Tool Partition Wizard" and used that to expand the "C" drive to the full capacity of the new SSD.  
 
Also, contrary to what I was told on the Dell forum, the cabling (power and SATA data) and hard disc carrier are there if I ever wanted to install a hard drive or full size SSD.
 
Resplendence Latency Mon shows the Laptop is "clean" for audio.  I plan on using it for on site recordings but only for the recordings.  They will be transferred to my desktop DAW for processing.   

fireberd
I bought a Samsung 500GB M.2 2280 SSD for it.  Opened it and replaced the original 250GB SSD.  I had a Macrium Reflect full disc backup and restoring to the new one went with out a hitch. 

Same here. For some reason the 250 filled up way too fast for my liking. With the 500 I'm only using 110GB. Not sure what happened there. The migration to the 500GB was a total fiasco costing me over $300 to fix so now I'd think 2x before doing it again. The original 250 stores all my samples and instrument libraries.