https://www.ddo.com/forums/showthread.php/275144
that thread is out dated because TWF animation has been changed, but I would say it still close enough for an approximation (could be wrong haven't thought about it and what the change really means ...)
Look at the chart on the first post
Staffs are fastTHF and 15+15=30% alacrity = 113.3 swings per minute = 113.3 attacks per minute. (1.88 attacks per second)
Khopesh is standard TWF at 15% alacrity = 118.5 swings per minute (assuming only 80% offhand proc rate) = 118.5*1.8 = 213.3 attacks per minute (3.55 attacks per second)