Depends on how cold the room gets at night. I use a 65 watt RHP on a Herpstat on my 4x2x14 Proline in a 75F room and it works fine. So I would imagine a 60 watt CHE would work fine on a V400 assuming your night time room temp is the same. As for running it during the day, either use a t-stat on it or a lamp dimmer and dial it in during the day when its the hottest. Should keep it warm enough in the night then when the temps dip. Have to just mess around with it on a lamp dimmer unless you are using the t-stat. As for the 40 watt, should work. If you are buying them local, most pet shops will let you exchange them if they aren't big enough. It just means more money for them.