The answer depends on what you are looking for.
For this test I used am M200 steel (gold plated) F nib, and two 14K M400 and M600 F nibs.
So how thick are the lines?
If you are interested in a true F nib that produces a real fine line, then the M200 nib is the one for you. Unfortunately (as seen in the pic below) the M400 and M600 nibs write on the thicker side, so if you are new to Pelikan and want a M gold nib, order a F gold nib, and if you want to write fine lines, order an XF gold nib.
I tested a 1960's Parker 45 F nib just to get a different perspective. The Parker 45 wrote somewhere in between the thickness between the Pelikan steel nib and the Pelikan Gold nibs; proving that the M200 F nib writes a true fine and that the M400/M600 F nibs write like a regular M nib.
Are they flexible?
While I have heard that the Pelikan nibs have some flex, I could find none. The M200 does have a bit of springiness which makes the nib feel softer and more pleasant to use, but comparing them to a true flex nib such as the one in my A.W Faber Dip pen from the late 19th century, it is clear that the Pelikan nibs don't produce any real variation and can't really be considered to have any flex.
The closest one has to be the M1000 (which I used to own) but that one just has massive amounts of springiness, but can't produce lines with enough variation to be called flexible.
The M400 nib was a dissapointment:
While the M400 Gold nib writes smoothly and has great ink flow, if you look at the picture below you will see that the M400 nib has a wider cut as it gets closer to the tip than the M200 and M600. This is probably why the M400 seems stiff as a nail in comparison to the M200 and M600 nibs, which have a pleasant springiness.
From left to right: M200/M400/M600
The M200 nib is larger and and has a narrow cut that gives it a very sharp appearance as it tapers towards the tip and I suspect gives it the springiness. The M600 nib also has it, however, the M400 nib is shorter and wider towards the tip which is why I suspect it feels more like a nail.
Here is the M200 up close, notice how the nib narrows considerably as it gets closer to the tip. The M600 is just like that, while the M400 has a wider and shorter cut.
While there are some reports of the gold plating of the M200 nib wearing off, I have yet to see any wear in my M200 nibs after mode than a year. I see no difference in construction quality of the nib and the M200 performs just as good or better than any Pelikan with a Gold nib.
Pelikan steel nibs (at least in the M200) are just as good as Pelikan Gold nibs, and the springiness of the M200 make it a better nib than the M400. You'd have to go up to the M600 to find an equaly springy nib with as much character as the M200 nib.
The following might be very controversial but I need to say it:
If you are considering a Pelikan and you like a springy nib with a lot of character, get the M200 and when you are ready to move up, skip the stiffer and more borring M400 nib and buy yourself a Pelikan M600 instead.
Edited by Dr Ozzie, 26 December 2008 - 20:30.