If you think you're a super gun scalper then you've gotta try these games

http://reflextest.net/reaction/color.htm
http://reflextest.net/reaction/clock.htm
http://reflextest.net/reaction/average.htm
http://www.maniacworld.com/Test_your_reflexes.htm
BTW, don't dishearten if you're slow at these games, you can still be a great scalper.
Recently I was reading 'Bounce' by Matthew Sayed and he mentioned that his reaction time was about 150 ms in the game of ping-pong but he still couldn't get a racquet on the ball trying to return a 350 ms tennis serve. He wasn't slow, turns out that he didn't know what to look for i.e. the vital signs.
Here's a little tip to improve your reaction time in the first three games - click and hold the Stop button immediately, but release it when you see the image/number flash on screen. I was able to improve my reaction time by 0.110 seconds by doing that

Good Luck! Hope to see some great scores on this thread!