Hey all.
Some time ago I also suffered severe FPS and lag problems. My FPS was about 15 at the fleet and about 40 outdoors.
That's my system (2 yo):
Processor: Intel core i7 920
Motherboard: Gigabyte UD4 (Intel X58 chipset)
Video: Radeon HD4870
RAM: 6 GB
OS: Windows 7 Professional 64-bit
I was very confused, 'cos in beta my FPS was up to 120. I was very disappointed until I changed the graphics settings from Low to High with all effects on except shadows.
Now I've got 50 FPS at the Fleet and about 90 outdoors. In fact, the same FPS is provided by latest GeForces my friends use.
The conclusion I came to: most in-game performance issues are caused by software, not hardware.
All above proofs this, IMO: