@ican711nm,
Since you haven't defined X, W, Y or Z there is no way to answer your question.
Are W and Y in ppm or in grams or some other figure? What figures are you using?
Lets assume that W and Y are the same. That would mean that X and Z would depend on which is greater would result in which equation is greater.
In reality, you leave several things out of your equation. An increase of W won't cause an increase of X always. It depends on the amount of water vapor that is there before. The more water vapor there is, the more IR that is absorbed but only up to a certain point. At some point the existing water vapor will be absorbing all the IR so adding more water vapor will have no effect on the amount of absorption. What happens at that point is you heat up the lower atmosphere because more of the IR is absorbed in the lower atmosphere with less being able to transmit to the upper atmosphere. So, even though the amount of IR hasn't changed, where the absorption occurs has changed.
The same thing will occur with CO2 but CO2 starts with a much lower concentration so it will take longer to get to the full absorption in the atmosphere.
So, in reality, sometimes x/w will be greater and sometimes z/y will be greater. Without values from you, there is no answer to your question.
So, to put this in perspective, W could be increase 100 fold more than Y but Z could still be greater than X. Without values, your question is meaningless.