You should start a sprint at your cruising RPM -- I like to start mine around 100 rpm. Once you start, it is unlikely that you can shift and still win the sprint -- I'm talking about after you pull off the last wheel, and it's just 150m of air between you and the finish.

If you are capable of spinning up to 160 rpm, and start your sprint at 100 rpm, you should have plenty of headroom. A flat sprint will likely start at over 32+ mph after everyone goes early or executes leadouts. From 100rpm at 32 mph, you won't run out of gears until around 50 mph -- so you won't run out of gear. If you start to feel like you really are spinning out, lock your ankles (don't let them bend) and you'll get another 5-10rpm right away -- but that trick is only good for a couple of seconds.

Training for sprints is a different story... though some of your training should be near race conditions so you know what it feels like.