This is a poll of sorts. I noticed more or less by accident that no matter how little or how much I over or underclock my CPU Rift always uses 28-33% of my CPU's output. It seems to average at about 30% or 31% but will spike up to 33% and down to 28%.
At 3.2 GHz, stock clock multiplier and FSB, the game used 30% or so of my CPU's output.
At 4.0 GHz, stock FSB and 20x CPU multiplier, the game used approximately 30% of my CPU's output.
At 3.875 GHz, 250 MHz FSB and 15.5x CPU multiplier, the game is still using only 30% or so of my CPU's output.
So now I'm curious. How much of your CPU's output is Rift using or at least allocating?
If you don't know how to load up Windows Task Manager it's quite simple. Just press Control + Alt + Delete. In Windows XP there'll be a button labeled Task Manager. In Windows 7 it'll be a quasi-button thing labeled "Start Task Manager." I'm sure in Vista it'll be something similar but I've no idea what since I never used that... OS. Alternatively you can just click Start and in either the search field (Windows 7) or file box after clicking Run (Windows XP) type in taskmgr.exe and run the program that way.
Next just click on the tab labeled Processes. You may have to sort the processes in alphabetical order as sorting by processor usage can cause things to move around thereby making them harder to find and read. Once you've found rift.exe watch it for a few seconds until you can get a rough idea of either the average CPU usage displayed or the usage number it sits on the most.
Afterwards please feel free to post that number, your CPU model, and current clock speed here. It would also be nice, presuming you have the skills to safely do so, if you could under/over-clock your CPU and report the CPU usage values for as well as the adjusted clock speeds.
My theory is that at least for some hardware configurations the game itself is proving to be a bottleneck to performance. The fact that CPU consumption by rift.exe regardless of my CPU's clock speed seems to bear that out by indicating that the total percentage of system resources it's allowed to access at any given time is limited. My hope is that enough posters will see similar CPU usage values that either remain the same regardless of over/under-clocking or that are within a few percent of 30% to determine a trend.