You could definatly go sata on the hd, i did that in my system and ran a raid 0 stripe, and increased my game load times by leaps and bounds.
The timing on the ram is weird.
You can never go wrong by stepping up the power supply, most overlooked peice of hardware in a computer. People dont realize how important this is. There is so much to explain about the importance of the PSU that its something people should spend some time to read about for themselves, and im not talking about watts.