Had a very similar issue last night. Turned out my CPU overheated and broke the plastic clips that hold the cooler in place. Almost certainly not what your issue is but I think component temperatures are often overlooked when searching for performance issues. Most boards by default will shut the system down at 100C. Intel CPUs (can't speak for AMD) however will start to degrade performance at around 80C. This becomes even more of an issue when a game like Defiance uses more of a certain component (CPU in this case) then what most other games do.
Also checking your drivers as many others have pointed out is a very good start.
To give you some context, I run the game just fine on my laptop (since I'm waiting on a new CPU cooler) that has peanuts inside it compared to the specs you posted. (GTX 660M, Core i7 3630QM, 8GB).
It's also worth noting that if your system is chewing on the hard drive in the background it could severely impact your frame rates.
Obviously you're more than welcome to stick to the "It has to be Trion" reasoning, in which case you'll never get to the bottom of the issue. But it's important to note that when the vast majority of players have no issue running the game on lesser hardware it kind of limits the possibilities in determining a cause for the issue.
I've already gotten to the bottom of it. The game is poorly optimized and I'm sure Trion knows it. Just because some people cannot tell the difference between 60fps and 45fps doesn't mean that there are no issues. The engine was obviously made with console limitations in mind, and as such they didn't spend much time making sure the game utilizes modern GPUs which explains why shadows and high details (which btw do not affect texture quality only shadow resolution, tree foliage and view distance) are such a huge performance hog. For the moment all you can do is to disable shadows or to set details to medium.
actually i can tell the difference when its under 50hz - i get headache after a few hours of gameplay.
I feel bad for OP if he's having these issue's but I'm with others here in saying I'm not having these issues at all. My rig is below average, I built it myself about 2 years ago and most of my components are at least a generation or more old and I run the game fine.
You should take a look at my youtube chanel little kiddy
http://www.youtube.com/watch?v=FXFU4P_dQ50
so you can see me put my gtx680 in my computer and youll also be able to see my massive Havik 140 cpu coller and one of the best airflow cpu coller![]()
when i say the game is stuttering the game IS stuttering on the highest setting but not on medium and low ones![]()
When people say it's your computer, they're not necessarily saying your computer isn't powerful. They're saying something about the combinations of specs in your computer have some type of conflict with the game. Calm down. Submit a ticket. Wait.
Try to be nice when someone tries to help you. You did post it in a forum after all. XD