Even though even the recommended sys req's aren't too intimidating, Total War seems to be a real bear to max out for even the strongest systems. I don't personally play it, but everything I've read suggests you need a pretty high end rig to come close to maxing it, even at 1080p. I haven't seen it said anywhere, but my guess is just poor optimization.
As for the original question, yeah, clock speed is just a number that doesn't mean a whole lot at face value. Don't get caught up in clock speed numbers, and anyone that tells you that's all that matters just doesn't know what they're talking about.