Given that this is a port of a game designed for 6-year-old hardware, that's a pretty good indication that the port is poorly optimized.
I really wish people who've never had to do something like that would stop making assumptions about how easy it is. It may be "6-year-old hardware", but it's 6-year-old hardware that is static. Developers know exactly what they can make it do, and exactly how to optimize things to get the most out of it. They don't know how to do that with your 3+ year old system. All they can do is make the game able to work on generic PC hardware, and hope that your hardware is sufficient to run it. Sure, those with current generation systems can get more out of it, but assuming that your system should
automatically be better just because it's newer than an XBox/PS3 is stupid. And assuming the port is "poorly optimized" because it doesn't work well on your particular hardware configuration is a very narcissistic viewpoint.