Thanks. I am driving the Apple cinema display with 1200 resolution so it is slowing things down for sure but it hasn't been that laggy on Mavericks like it is in Yosemite. They need to address this in the x.1 update.
I see, just for completeness I'm driving two 23 inch monitor at 1920 x 1080. I don't have a good understanding of performance vs. screen resolution. I suspect the higher the resolution the harder the computer has to work. Not sure how those compares to the Apple cinema display.