CFS3 is a very unique animal in that it can have very high levels of scenery density and terrain resolution - the engine really was waaaay before its time and it is hardware limited.
The caching seems to be O.K but it could be better and what it happening when you see the lags or micro second pauses is the HD light flashing as CFS3 loads up more into memory or swaps in and out of memory.
Two main ways to reduce:
1) Turn down the Scenery and Terrain sliders.....mmm not nice...
2) Improve HD access time.... as many have realised this is one solution to the issue... SSD would be an amazing solution.... if its affordable go for it!
Ideally all required data for a sim should be preloaded into memory, but CFS3 covers a vast theater and with a high level of detail - so this seems to be its limitation to a certain degree but I can say we have seen CFS3 run better and better in this respect as hardware improves (since 2002 wow).
By balancing the sliders and hardware many have seen that it can be brought to a point where it runs pretty smooth as many users as well as the dev team will attest to
One thing you can do is the classic external rotate around the craft at mission start - call it a craft pre flight check - which forces CFS3 to load more into memory of the surrounding terrain and hence you will have less micro pauses as you fly out.
Also yes quit as many background tasks as you can!
HTH
WM