The cache can kind of act like a bottleneck for information flow in your computer, so a bigger one will help information flow faster. It also sounds like your computer habits would be quite demanding on RAM, so that is likely part of your problem.
Remember EVERY program has files (subroutines) it loads into your (limited) RAM space every time it is running. As all programs try repeatedly to access their own subroutines they can interfere with one another when RAM space is limited. Thus, for the meantime, you would likely have better performance running fewer programs at a time.
The number of browser windows minimized may or may not affect things. If they are entirely 'passive' windows, they won't affect much, but many will be trying to run java scripts you are not aware of, so try and reduce the number of windows you leave open as well.
ABE: It occurred to me you may have a damaged file in your operating system. Have you tried using 'system restore' to take your computer settings back to a date before you started having these problems?
Note: this will not be possible unless you are running XP.
Edited by EZscience, : No reason given.