Eist is your speed step, it slows down the processor and lowers voltages when you are at idle. Definitely enable that.
C1e, C1, C2, C3 are mild sleep modes, they do most of the sleep shutdown work and should be enabled.
C4-C6 will depend on your psu and bios. You have a Haswell cpu, which enabled ultra heavy sleep modes with very little actual voltage used, it's so low that many older power supplies are incapable of waking up afterwards. It's almost like the pc goes into a coma, still on, just can't wake it up. If you have the old style psu, it'll have large green/white lettering CS650. Don't use C6/C7 with that psu. If that means your bios stops at C3, and you don't use C4+, then so be it.
If you have the newer design psu, it will have black/grey design and you can use all the sleep states as those psus are Haswell capable.