I can tell you that the reason I don't use Fusion-io cards we have as boot devices:
- Cost/ GB higher than SATA SSD - Intel 320 or S3500 is much cheaper per GB
- Lack of kernel driver support means it's way easier to install the OS then Fusion-io drives rather than trying to do both.
- Speed - you don't need PCIe SSD for boot
- Service - if you need to upgrade firmware for the drives it isn't like using a SATA driver
- Compatibility - even NVMe drives on some motherboards have issues booting from them. Avoid that hassle.
If you're running Linux, Solaris, VMware, Hyper-V Server 2Kr2:
Intel S3500 80 GB,Internal, 2.5" (SSDSC2BB080G401) SSD is what you want for an OS drive.