How fast do you need to sample? That particular hardware should be fast enough, but looking at your VI, you are creating a new task each loop using DAQ Assistant, which is very slow. Also, trying to get your elapsed time by placing the Elapsed Time Express VI inside your while loop (which again the express VI's are really slow), you are actually making your loop take longer to run. If you want to know how quickly your loop is running, look into benchmarking your code.
