XPS 8900

32GB SSD is a joke.  IMO, a 256 G SSD is right on the edge. I am running 500GB SSD and find it is perfect .No need for anything larger. I was considering that machine but I was able to take the one I bought with a 1TB hard drive, and do upgrades, BR write, 500GB SSD and have the price cheaper.

I have the 8900 with the 32GB SSD.  I got a great deal (~$780+tax - another $78 cashback using Discover Deals) on a system w/ 16GB RAM, i7-6700k, wireless AC, and a 2 TB HDD with the 32 GB SSD (no monitor).  The SSD is configured as a cache drive so it doesn't show in the file explorer and there is no OS or other programs on it.  However, my understanding is that the 256GB SSD does because it's not configured as a cache drive.

If it wasn't for the deal I got, I probably would have gone for the more basic 8900 configuration (just a 1 or 2 TB HDD) and added a 250GB (or larger) SSD myself.  If you feel comfortable doing this kind of stuff, it seems to be more cost-effective than buying it with the 256GB SSD from Dell.

This is most likely a hybrid drive, 32GB SSD with 2TB's of normal HDD, I don't see why they would even offer them separate, as 32 is just too small, it prob... use's the SSD as a cache to speed up normally used programs and help with boot time. If the SSD is separate its mostly likely the OS and everything else is on the HDD.

the whole reason for 8900 = Skylake i7-6700/K (allows 1 m.2 standards, & more importantly increase in PCIe lanes &/or bandwidth) this allows you to take advantage of the "NVMe" SSD's via PCIe only, the Dell OEM m.2 slots are only 1 lane (1 lane will not allow full bandwidth and will only allow up to 800reads/800writes) you need 4 lanes to get the speed hence the PCIe 3.0 x4. which has a max bandwidth of 4,000reads/4,000 writes "theoretically" 

I myself am getting 2500+ reads/1500+ writes on my Samsung 950 Pro 512GB, the reads are 5x faster than a SATA SSD, and 3x faster on writes.