Hi E.,
You have the right idea. While sleep duration varies a lot from child to child, the average is around 10 hours at this age, an hour less and you start to see adverse consequences, such as overweight (see http://cme.medscape.com/viewarticle/568253 for a more medical/scientific description of it.)
As a peaceful productivity specialist, I study everything about sleep since it impacts productivity. It seems that the majority of us adults are sleep-deprived at a level or another, and we're starting to do the same thing to our children. It often comes from wanting to see our children after a long day at work, but it hurts them...
My son is almost 7, and we have the following routine: in bed by 8 - 8:10, lights out by 8:30. He wakes up on his own around 6-6:30 in the morning, a sign that he's slept enough.
This being said, let me add a caveat: some kids are naturally night owls, and 8 PM is way too early for them. You know you have one of those when your kid has trouble falling asleep before 9-10, and you have to wake them up in the morning or they'll sleep until 8 (a friend of mine's daughter is like that). If this is your child, see how you can make the morning routine as short as possible, so that instead of waking him up at 6:30, you wake him up at 7 or even 7:30, and give him a bedtime about 10 hours before his wake-up time. If he has trouble falling asleep, say that it's ok, he doesn't have to fall asleep right now, but he needs to stay in bed calmly, with the lights off until he does fall asleep... If nothing else, this will develop his imagination. :-)
You are doing exactly what's best for your child in terms of his development and his school results, I hope the above gave you more ammunition to stick to your guns.
Let me know if there's anything else you need,
K.