Unless it's an old i5 (pre- 1150), you might have power saving features disabled. Haswell and Skylake / Kaby CPUs overclock just fine with power savings on, but you gotta enable them properly in BIOS (had 4770k@4.6 and then 6700k@4.8 and in both cases the idle power consumption was pretty much identical to a non-overclocked system). It's all those "C states" that are usually disabled by default, if you enable them the board+cpu+ram shouldn't take more than 40-45W. A couple of spinners would add 15-20W at most (or even 0W if they're powered down when you don't access the files from them). Coolers' power consumption varies a lot though depending on the size and rpm.