It really comes down to personal preferance. Personally, I would go with the Parker 51. It is famous for a reason. And Jack, if you know of a place to get cartridge filling Parker 51s without costing an arm and a leg let me know
From what I hear, they were made for just a few years and are quite rare. I would love to see one. I do believe that a Parker 51 would be the best pen for your situation although any would do nicely. The nibs are well made, very smooth, and very firm. The nibs are usually somewhat dry writers which makes the ink dry faster and prevents smudging when writing fast. The hood over the nib allows you to leave the pen uncapped for a good amount of time without having to worry about the pen drying up. It is extremely well made and should be able to withstand quite a bit of abuse (certaintly more than a modern 149). Some people don't like the look of the hooded nib, others do. The nice thing about the hooded nib is that it certaintly doesn't look flashy. If you get the Pelikan or Montblanc, even if the barrel is plain black, the big flashy nib will draw people's eyes. The hooded nib isn't flashy at all and if you get the pen with a stainless steel cap, the pen looks even less flashy. The sleek form of the pen I personally find very elegant. The Parker 51 is also known for holding a ton of ink, so you shouldn't run out of ink often in the middle of a meeting. Also, you can get a 51 for much less money than a Montblanc 149 or a Pelikan m805, so you have more money for ink and more pens. For the same price as a 149 you could probably get a Parker 51 and a Parker 75 (which is my second favorite from your list). It is nice with the 75 to be able to put in a new cartridge in the middle of a meeting. People might start looking at you funny if you pulled out an ink bottle in the middle of a meeting to fill up your 149 or m800, or 51.
Let us know what you decide
-Jesse