While I am all for helping people try to improve the game performance, there's a lot of bad/useless advice being given here. And a lot of people that don't seem to be reading the details in the original post. Before I start addressing that, OP, I will say that if you are seeing noticeably poorer performance than you did with a previous build, I would make sure the devs are aware of that. I also have to point out for the record that your computer is sitting at the MINIMUM system requirements and Beta's typically are not completely optimized. I'm not saying you shouldn't even try to play it, but based on that alone, I wouldn't expect it to run WELL, especially not with larger maps and/or higher AI player counts.
1) Page File/Virtual Memory. Several people suggested increasing that and I wish they would stop doing that. Based off the sysinfo you posted, your page file is currently roughly 12Gb and you have 4Gb of system RAM. Microsoft recommends 1.5x-3.0x your system RAM. You're already at the high end of that. In addition this isn't a magical fix, you can't just keep increasing the page file size and make all your problems go away. While that MAY prevent some things from actually crashing, the page file is SLOW. Your hard drive, realistically, is probably transferring data at around 80-100MB/s. DDR3-1066 is rated for 8,500MB/s. I'm not even going to touch the latency difference. Page file doesn't eliminate the need for more RAM. If you're exhausting a 12Gb Page File, you are simply trying to do too much with your computer.
2) Upgrading your hardware. Ryat mentioned the upgrade he did on his system and as far as what you can do with your current system, that is about the best you can do. More memory and more cores. There is the risk though that the BIOS version on your motherboard may not support a newer Core 2 Quad without an update (specifically you need revision F13 on your board for a newer processor). That's something you'd want to check before buying a newer processor. However, your system is 5 generations old at this point. I would strongly recommend against dumping any money into upgrading a system of that age, it's simply a bad economic choice. Even a low end new system (or a used but more recent higher end system) is going to out perform that, use less power, and generate less heat. If this is an option and you are willing to post a budget, I would be happy to provide advice in that regards. For example NewEgg has a bundle right now for $290 (plus OS) that would blow your system out of the water. Alternatively, keep an eye out on eBay and your local Craigslist for a bargain on a X58 based motherboard combo. The boards are running a bit of a premium right now, but you can get hex cores for them for dirt cheap.
3) Power settings, Raiding hard drives, overclocking, hyperthreading, upgrading Windows. No. Just no. It's a desktop computer. There's nothing you're going to do in power settings that will make the computer faster. Raid? Ignoring the technical risks and requirements in running Raid0 (which is the only "raid" that flat out improves performance so I assume that's what was meant), unless you're saturating your drive's throughput it's going to make little to no noticeable real world performance difference. Sure, load times may improve slightly, but that's pretty much it. An SSD even on SATAII would make a far larger difference. Overclocking? A system of that age? Without knowing any details like CPU cooler, power supply, etc? That's a good recommendation to get somebody to fry their system. Hyperthreading? Yeah, totally not a thing on Core 2 Duo's. Upgrading Windows? I don't even know where we are going with that.
The first step in improving performance is to figure out what's limiting your performance. If a program is GPU limited, all the CPU overclocking in the world isn't going to help. GalCiv is a bit outside the norm in that regards. Most AAA titles are shooters and are much heavier on the GPU requirements. GalCiv is exceptionally CPU intensive. It's also pretty thirsty for RAM in it's current state, although that should improve some as time goes on. But it's always going to be CPU intensive, that's the nature of the game. Eliminating background tasks can help with this but that will only do so much. You also have to be careful not to disable programs you actually need.
Before you launch GalCiv, bring up task manager. How many processes do you have running and how much of your RAM is being used? That will give is a rough idea on where to start.