technikok :
Without using a PCIe expansion which is the right m.2 SSD so i can take full advantage of m.2 slot on my mobo and don't loose speed?
IF I understood your question, you're asking which PCIe SSD won't be limited by your M.2 socket - even the xp941, 1st gen, which was PCIe 2.0 x4, was limited in my M.2 socket - when in the M.2 socket, max speed i saw was 770 MB/s read & 580 MB/s write. Moved to a PCIe 2.0 x4 expansion slot, i saw full speed, 1180 MB/s read & 870 MB/s write. There's not a terrible lot of economy, price wise, buying a xp941. You could check pricing on a 850 M.2 SSD (but it's sata, not PCIe), but don't expect anything above sata speeds, maybe 560 MB/s read - not sure what write speeds to expect