i have the 6850 with an X99 msi motherboard, pcpartpicker gave me the same warning, but I did not have an issue.
I would recommend an NVME drive over the SSD you have.
I would also recommend a 1080ti over the Xp.
The HD recommendation is based on my setup. I think the nvme helps alot with file read/write operations. A 1080ti should be cheaper in theory than an Xp and may perform faster. Refer to this thread.