most motherboards add a little extra core voltage over what is selected to increase stability
having it set at 1.825 is reasonable, and as long as you have good cooling and the chip isnt running to hot it shouldnt hurt it much.
i/o voltage increases the Ram voltage, the only time you might need to increase i/o would be if you are overclocking the fsb (not multiplier) and your ram is the the limiting factor then an increase in i/o might help you get a little more mhz, but it will also make your ram run hotter and decrease its life some.