4GB would be the bare minimum I would recommend for a Win 7 machine. You will see a significant increase in response speed going up to 8GB, and then a diminishing return to about 16GB. After that, unless you are running several very intensive programs, you will not see any speed increase.
Here is a video maybe explaining it. The guys t-shirt says “Holy Balls” so you know he is an expert.....
https://www.youtube.com/watch?v=ajyzZ-zaq0o
That’s pretty spot on. With the advent of fast SSD hard drives with their disk accesss and I/O the need more ram isn’t as high as it was 10 years ago.