Needle size is an indicator of line width, but only because that also changes the taper. Neither as mere numbers are going to give novices any clue other than the smaller the size, the thinner the line.
Badger describes their needle sizes as Fine, Medium and Heavy, which tells the novice no more than a number would. However, they also give you this guide:
• Fine (F) - pencil line to 2" (51mm) spray
pattern
• Medium (M) - 1/32" (0.8mm) to 2 1/2" (63mm) spray pattern
• Heavy (H) - 1/16" (1.5mm) to 3" (76mm) spray pattern
I have yet to see a corresponding guide from any other manufacturer.
As you can see, there isn't a huge amount of difference at the narrow end of the spectrum (and how wide is a pencil line? Is that based on an freshly sharpened HB (#2 1/2) or what?), but a bit more at the wide end. And there is still no indication of how far away the needle is from the surface to achieve those sizes!
There are just too many variables to be precise in predicting the pattern without testing. The distance from the surface to the needle and air pressure makes as much or more difference than the needle size. Even the medium used and the the amount of thinner to paint can affect width.
The point is 99% of the time, it barely matters what the needle size or taper is. Very few modelers have the need for pencil thin lines, and most of us are spraying flood coats at around 1" - 2" is width, and all sizes of needles will do that.
Needle size is more an indicator of the difficulty spraying a relatively thick medium like model paint. Clogging tips becomes a greater issue, possibly requiring filtering the paint to remove lumps and a higher thinner to paint ratio, which can invite tip dry with acrylics.
I recommend medium sizes (.4 or .5mm) as being more useful to
modelers OVERALL. I've not come across a need for smaller than 1/32" or
wider than 2 1/2". I have two 100LGs, one Fine and one Medium, and it's
the Medium I use most. I also have a single action 200-20 with Medium
and I can spray a thinner line with that than either 100LGs! Which is
entirely due to my inability to use a dual action airbrush and hold a
thin line consistently. 
If you've already bought the Evolution with the .2mm nozzle/needle and are having troubles, you can buy the .4m nozzle/needle as parts. It just costs more to buy them separately than buying the 2 in 1 version.