Answer to "Upgraded to 512GB SSD, now SSD link width down to x2 from x4?"I have had issues with my upgrade to Samsung 970 Pro 1TB with Sintech adaptor of lanes and sink speed dropping. See here. Please confirm if this PCIe SSD would work with my 2015 system I found a reset to PRAM allowed it to return to the full 8GT/s and 4x link width. Obviously you will not be able to get a faster or wider link than the slowest bit of hardware in your chain. eg I put the 512GB SSD from my 2015 15” rMBP into a 2013 iMac and despite the SSD being capable of 4x it will only get 2x link width because the iMac is only capable of 2x. Point here is for a machine that you know is capable of faster, the PRAM reset fixed my issues twice.
Answer to "Please confirm if this PCIe SSD would work with my 2015 system"For the benefit of all wanting to upgrade, I would like to confirm my successful upgrade of Apple Macbook Pro 2015 15” 2.8Ghz 512GB to Samasung 970 Pro 1TB using Sintech ST-NGFF2013C(ordered from this ebay listing ) and looks to be this listing at the Sintech shop Sintech ST-NGFF2013C(Sintech shop). The stock drive was an Apple 512GB Samsung that was running at the full PCIe 3.0 with x4 Link Width(4 lanes at 8GT/s) shown in Apple System Profiler. Speeds in AJA System Test Lite were around ~1500MB/s write and ~1850MB/s read. After install of Samsung 970 Pro NVMe 1TB, I at first got PCIe 3.0 x2 Link Width( 2 Lanes at 8GT/s). I then reset SMC and changed to a second adaptor (I had ordered two from Sintech of the exact same type) and rebooted and got the full x4 Link Width. Speeds in AJA System Test Lite with x4 Link Width ~2550MB/s write and ~2250MB/s read. Speeds in AJA System Test Lite with x2 Link Width ~1500MB/s write and ~1500MB/s read. I have been able to swap back and fourth now and get x4 link width...