Samsung 960 PRO is M.2 form factor (internally a 4xPCIe3.0 interface) with NVMe revision 1.2.
The rated specifications of this drive are up to 3500MB/s Read and up to 2100MB/s Write, which is pretty good (this interface allows a theoretical maximum of 3938MB/s total Read/Write throughput).

Intel 750 is a PCIe or SATA form factor (4xPCIe3.0 interface or SATA3 interface) with NVMe revision 1.0c. An M.2 adapter cable is included to link the SSD into the motherboard M.2 slot.
The rated specifications (on the best versions) of this drive are up to 2400MB/s Read and up to 1200MB/s Write - but only with the link adapter plugged into M.2 slot.
Without the M.2 link, these drives default to slower AHCI/SATA3 protocols.

NVMe is technically only an improved instruction/addressing protocol - it allows more commands to run more efficiently in parallel or in queue. It does not in itself indicate a faster, better, newer drive - although the faster, better, newer drives tend to include NVMe and advertise it proudly, the marketing confuses the consumers. NVMe isn't something that makes your games and programs load faster - a fast drive with fast specs will make your games and programs load faster (regardless whether it has NVMe or not).

In a nutshell, NVMe generally makes real-world performance a little better, more Read/Write data per second. It never hurts. But (like DDR4-4266 or 256GB memory capacities) it's hardware which is basically designed to optimize specific (and deliberate) usage scenarios the overwhelming majority of consumers will never actually use. Both of these devices (along with most other M.2/NVMe/PCIe SSD devices) are already "overkill" for gaming.

16xPCIe3 for GPU, 4xPCIe3 for Samsung SSD, 1xPCIe3 for Xonar = 21xPCIe3. Intel 750 requires 4xPCIe3 (plus M.2!) so adding it will muck everything around - and it'll knock your GPU to 8xPCIe3 which will limit gaming fps/performance under heavy load.

Don't buy into the hype. Intel 750 is good. But not as good as it looks: it was the "best" back when it was new, it's still considered the "best" by some Enterprise/Server folks who swear by Intel products and Intel support. But Samsung 960 is better: it has better specs, it's faster, it's guaranteed to last longer, it costs less.

Lets get something straight. Samsung 960/950 line is great for sequential reading large files, but not so much real world read/write of small files. The intel 750 has the IOPS that trounced the Samsung 950 and while the 960 is much better, in many tests, the 750 intel still wins.

Overall I think the Samsung 960 is a bit more flexible and better as the overall drive, but it all depends on how strict Intel will be on their whole VROC system. If Intel refuses to let Samsung, OCZ, WD and other M.2 manufacturers the in ability to use VROC to make bootable drives on their new x299 platform, then year, Intel is going to be ahead. This is especially true if Intel prevents the bootable drive from happening on the chipset side like happens with the z270 mbs.