In case that someone finds this useful:
After struggling for weeks I found that at least HP Proliant Servers DL320e G8 / Gen8 and DL160 G9 / Gen9 have a poor writing performance with Kingston SSDs (DC400 in my case) when the embedded Intel SATA controller is configured as "plain" AHCI or as SATA Legacy (IDE). The former misbehaviour does not ocur with magnetic hard disks.
Changing the mode to HP RAID (a.k.a. software / fake RAID) solved the writing speed issue for SSDs, just let the disks "unconfigured" in the storage administrator; no logical drives, arrays or whatsover were created.
By the way, this same situation arises with Lenovo Servers RD350, but this hardware has relatively "decent" writing performance in IDE mode and probably (not tested yet) also in software / fake RAID mode. Incidentally the RD350 has an embedded Intel SATA controller as well, which leads me to believe this is a bug of several Intel SATA controllers, since the servers I tested have different controller models and obviously the problem is multi-vendor (HP and Lenovo to my knowledge).
It is worth mentioning that everything was verified in Windows 2012 Server and Oracle Linux 6 and 7 ( Red Hat / RHEL / CentOS). Do not forget to keep BIOS and storage controllers firmware updated.