Well, with a block size of 100 elements I can set the rate as low as I want, but I am not sure it's really getting it done that fast...Excel is probably not the right way to test this...
EDIT: Well the biggest block size I could get to work in Excel was 122, so I not have 4 OPC links to get 350 REALs from a CompactLogix.
I changed the polling rate to 20msec and added a rung to simply increment one of them every scan. To my naked eye, it looks like its doing it at least as fast as Windoze can repaint the screen...