Okay, so 3 questions:
1: Do I need to clear the cache everytime I change the settings and restart the game? I keep trying to change the terrain detail and nothing seems to happen.

2: I've read the guide on Neoseeker, but I'm still unsure if those are the best settings for my computer. I turned a few down and the game runs at a decent speed, but the quality is terrible. I don't really know where my computer stands, whether I have wiggle-room for Medium or High detail for Sims & Texture.

What I'm working with:
OS: Windows 7 - Home Edition.
Processor: AMD A6-3420M APU with Radeon HD Graphics 1.50 GHz.
Installed RAM: 6.00 GB (5.48 usable).
Graphics Card: AMD Radeon HD 6250G, 4043MB of total memory, driver version 8.903.0.0.
Drivers: I think they're updated now.

3: I just saw another post recommend Overclock Nvidia. Would this work against my Power4Gear High Performance, or my AdvancedSystemCare Turbo Boost?