I just bought this game and I frequently freeze up for less than a second when moving around the map, fighting and zooming in. I've tried updating my graphics drivers, lowering the settings and disabling AMD crossfire. I have an AMD Radeon HD 5900 Series card. I had some problems with the previous Hegemony but they were solved by turning off crossfire for it.
I tried the game out on my work PC which has an Nvidia GTS 240, the stuttering only seems to last for the initial few seconds of a game here, then runs smoothly, despite this graphics card being a very cheap one by comparison.