Ok let me take a stab at this. You're looking for shots that stand out from the P&S crowd so that your party pics on facebook are the ones everyone links in their twits...tweets?
Here's the problem: When you / facebook / the iphone resamples an image for display in a tiny box, it changes the
circle of confusion...which, coincidentally, is the same term used for the group of people you're photographing standing around the dude laying on the floor in a pile of broken glass because he passed out and fell into the coffee table after holding his breath too long after that monster bong hit.
But I digress. You like the FA43 because it has a narrower
depth of field (DOF) which is much more apparent on tiny screens than the wider DOF of the FA31 shots. Back to the point above, resampling the images actually makes them appear to have MORE DOF than they do at full (or regular viewing size). That's why blurry images look sharper when they are resized, or you view them from further away.
So that's all there is to it. At internet sizes, other lens characteristics like sharpness, colour,
chromatic abberation and so on get thrown out with the bong water. So...if you want narrow DOF to get your shots noticed, get the longest lens you can reasonably hold with your right hand, 'caus chances are you won't want to put down the 40 of JD in your left.
Make sense?