The answer to this question is "more than I'm getting" !
You don't realise how much you value your sleep until you have little influence over how much you get - it's not as simple as going to bed early, since there are other factors, some of which I would rather not discuss, preventing me from sleeping as long as I like. At the moment I have to survive on between five and six hours but would prefer to get 7-8 hours. Anything over 8 hours is a distant memory. Having said that, I can fall asleep at the drop of a hat and regularly do on the train home. Even if it's a 20 minute PowerNap, I find it helps.
I would be a brilliant case study for the effects of long term sleep deprivation.