I believe to claim it's DDR3, it has to be able to support running at 1.5V, if the system doesn't support 1.35V then it'll just run at 1.5V, if the system supports it, it'll just use a little bit of power and put less strain on the IMC in the CPU, I'd think that a P55 board probably supports 1.35V if you have the most updated BIOS. either way it'll work, just if it runs at 1.5V it may use a virtually unnoticeable amount more power and dissipate a mostly unnoticeable amount of extra heat but the difference between running the ram at 1.35v or 1.5v will cause no noticeable difference, the push to 1.35V was mostly when they got to 32nm and smaller transistors as 1.5V+ ram puts more strain on the integrated memory controller and can possibly shorten the life of the chip, 1.35V memory wasn't a requirement until Intel got down to 22nm.