Well, from experience, once you load the game with high level textures, while it's running if you switch to low settings, it doesn't always work out that the textures end up being low res.  A habit of mine is to save, switch to low settings, exit the game, restart, reload, then continue on.  Another thing is when you're seeing 50% total processing, does that mean 50% of one core or 50% of both cores together?  Sins runs on a single core during game play and you're more then likely maxed out on the core it's running on while the second core isn't doing anything at all showing you that you're only using half of your CPU's total power.  That would be the main bottleneck in the game at this point.

Depending on what version of the game you're using, tricks to improve performance are reduce the number of strikecraft, reduce the number of mines, reduce the numbers of trade and refinery ships, and unpin things from your empire tree, and the most fun trick is to kill off a faction, especially the pirates.

its 50% of both cores. (dual core). I may need to upgrade processor.

thank you.