CPU requirements are always bullshit as the CPU is a non factor in PC gaming. I suspect Intel/AMD pays to get the CPU in the recommendations even though a 10year old mainstream CPU would do fine in every game. It has always been like this.
How is a CPU a "non-factor"? You think all games are GPU-bound? Also good luck running modern games on a single-core Intel Pentium 4.
Dunno why people are so surprised at high VRAM requirements. The next-gen consoles have 8GB of memory for both CPU and GPU access. What did you expect to happen when these games were brought over to PC?
Either Olga or the RAY fight at the end. Olga because it's early and you're limited to a small area while she's running around hiding behind things and lobbing grenades. You don't have a lot of options with that one; just gotta be patient, use the cover and make use of those opportunities. The RAY fight is more just endurance because actually destroying one of those things isn't too hard, but doing it twelve times in a row while avoiding getting killed by the others is tricky and gruelling!
The HD versions also don't have the pressure sensitive face buttons, which MGS2/3 use for various things (Gently releasing the Square button allowing you to put down your weapon without firing comes to mind).