Always go for the highest figure off the top of your head. Worst case they could say No.

In the normal world, your largest raises will come when you get a new job, and quit your current one. It's just the way it goes. You will always be seen as the guy that they hired at "B" price in thier eyes. When infact, you should be making "A" price. So, work hard and learn as much as you can at your current job. If you feel like making a big pay jump in 5 years, start throwing your resume around.