I'm going to have a go at an < 5 hours, no kill/continue/alert play through on big boss extreme. It can't be as hard as it sounds
It is, and it isn't.
I was surprised how easy it is to crawl past PMC soldiers, actually. Also, there are places you can literally run and not get spotted. Each stage has a safe path you must find to go quickly through that stage. There are still soldiers you must deal with, but they are few and far between and makes the stage very easy compared to searching the area for goodies and then confronting the soldiers you come across. Ignore them, go around them and they wont spot you.
However, I wasn't prepared for some 'boss battles' that were insanely difficult, like the 'bike ride' with Eva. I had do that over, and over, and over, and over, and over, and over, and over, and over, and over, and over and over, and over, etc. The Frog battle at Advent Palace wasn't fun for me, either. I hated all that waiting until they walked into my smoke traps.
A good tip for the 'bike ride' is to use chaff 'nades for the gekkou (it stops their missile and gun attacks), smoke and stun grenades for everything else, along with the Solar Gun and Mk. 22 tranq pistol. I've got plenty of tips, if you want them. Just let me know.
Personally, I haven't finished my Big Boss Emblem run, yet. I was missing some key songs that I needed, and had to play through the game again to find them. However, my iPod songs list on the BBE run didn't get updated, so I have to start all over again. Plus, I'm not sure if MGS4 will get trophies, but I'm waiting until I get the official word it will or wont to restart and finish my BBE.