What is the "real" difference in an Intel i3, i5, or i7 as far as speed is concerned?

What is the "real" difference in 4 megs ram and 6 or 8 megs.

What about Amd compaired to intel. Back in the day when I built a few desktops for my own use, I felt like Amd chips were more prone to lock up than intel, but it might have been the one I had.

Is win 10 going to need 8megs memory like win 8 does?

Mostly net running and storing a few pics, no gaming or other intense programs.

I'm all ears,

John