The original M600 was the same size at the 200/400 but had an 18K soft nib and more gold furniture. Of all the modern Pelikans it is my favorite.I was fairly adamant on getting the M600, but the past day or so, I have suddenly started leaning towards the M400 once more - that was the model I was thinking I would get when I went into all this.
The M400 is almost the same length as my Waterman in most respects, and posted, I would say the M400 seems to be a very well sized pen. As BMWRider said, it seems as though I prefer smaller pens, so why fight it?
In any case, I still have a few more days until I make my final decision, I'm leaving the purchasing to later this week.
Top down, old 200, m400, original 600: