i noticed a huge improvement in performance going from a 5 install to a 2 install

main char with all the addons in wow install 1

then my shamans with their own macros and addons in install 2

loading time on the 4 alts pretty much load in-game at the same exact time, my main lags a bit behind as there are more addons loading but it only takes a few seconds for the alts to load so its still pretty fast.

system is 2x200 7200 RPM in raid 0