Don't forget it isn't just raw watt savings. You also have the heat dissipation of that heat, and then the additional AC load and it's inefficiency. I'd multiply power savings by 3-4 if you want an accurate figure for amount saved.
Fans running at a bit higher RPM does not increase energy consumption in a noticeable way. A typical PC fan power consumption is about 2W. If you are water cooling without fans then there will not be any difference at all.
If you need air-condition at all then you must realize that these systems have COP of about 4. That means that increasing heat dissipation of your computer by X watts will lead to increase of air-condition consumption by about X/4. That means that your power multiplier of 3-4 is very wrong. If you really want to apply it at all (notice that in during winter you save on heating) then it should be somewhere around 1.25 - 1.3. That does not make a significant difference.