besides 16x16 is just too big, i started a few 14/14 embarks and my mind just boggled at the amount of space i had at my disposal, i balked just deciding where to put my initial settlement... also stonesense won't let me screenshot entire embarks over 5x5 so i'm on the fence about if i should make it so big, however i'm planning a human fort inspired by post Norman London , the town sorrounded half by wall, half by river, divided into 4 sectors, each containing it's own meeting area and megaprojects and it's own industries.
A military area containing a tower/fortress with most military related induistries, the meeting area being a theatre in the round.
A port containing a massive ship and most mercantile industries, meeting area being a marketplace.
A royal quarter containing the royal palatial residence, nobles, prison, legal stuff, hammerer, etc meeting area being the law courts.
And finally the main residential part of town containing a huge cathedral as well most primary industries (carpenters, masons, bakery, etc) meeting area of course being within the cathedral itself.
Farms, forests, quarries, mines will be outside the walls, quarries must be open pits for authenticity, no construction underground allowed except for basements, ore/coal mines and the digging for the docks.
Use of magma not allowed, except i may spawn some with DF hack for mood lighting or various superficial uses. Humans will be modded to allow steel and other industries nessicary for a complete fort, and some items will be removed.
Anyway back on topic, the space needed for the megaprojects is significant, an embark square just for the cathedral or the ship, and each resident will be given a tudor style wood and plaster house with internal space 6x3 and 2 stories (as humans each story will be 2 zlevels which will make the houses look better also) bottom floor containing whichever workshop the resident works at.
For this i should need a big embark area, 16x16 would be nice so i still have space for forests. Also i may mod plants to produce less food so i need more space for farms, shorter growing seasons also wouldn't be remiss.
er yeah good luck with your embark, on my 14x14 i had great fps but ram usage was at 1.8gb which i imagine would probably hit the limit and crash by the time i had started construction.. however i did leave the bottom layer on. i imagine your cpu use for a huge embark should be the same as a smaller embark as long as there isn't lots of extra creatures or flowing water