Then press space bar. If it stutters, increase the buffer size in File>Settings. If it stutters no matter how high you set the buffer size (probably don't go higher than 10240), then your computer might not be powerful enough. Try lowering visual settings in your OS. I find that my low end video card will run EOF faster when I am using 16-bit color depth instead of 32.
Edit:Newly-found bugs:
*Some condition exists that could cause bass drum (and possibly other notes) to be clipped from the 3d panel. Here's a screencap:

I have emailed you a set of files that demonstrate this problem.
*Tails that extend into a tempo change still only take their note's original tempo into account, they won't end on a correct snap to grid position in the ending beat
*Strangeness with modified indicator/undo system: If a chart is saved after edits, changing a note's tail will not mark the chart as modified until undo is invoked to undo the tail changes. From that point on, if another tail change is made, undoing it will not remove the modified indicator on the chart. Saving the chart one more time will reset the modified indicator but this cycle of weirdness can be invoked again afterwards.