Yes, 5.1.x or 5.2.x can go right to 6.0.5 firmware.  The matrix is in the Firmware Upgrade document for 6.0.x, not the release notes.   Regards, 
Just wanted to check with the community since I reviewed the release notes for v6.0.5 of the PS firmware and didn't see the "Supported Upgrade Paths' like the other versions have always had.   Am I ok to upgrade a PS4000 from 5.2.1 straight to 6.0.5? Or do I need to install an intermediate firmware version?   Much Thanks!
EQL PS4000 Firmware upgrade 5.2.1 -> 6.0.5 supported?