Our 777 flying manual suggests that, when permitted by ATC, you should exceed the 250kt limit at the earliest opportunity and climb at the appropriate ECON speed for the input Cost Index. A CI of zero equates to approx 280/0.82 and a CI of 100 gives approx 320/0.83.
Hope this helps. For those not familiar with a Cost Index, it's a figure input into the FMC which bases the most economic speed for the route on a number of factors such as cost and time. A cost index of 0 equates to minimum cost, a CI of 999 is minimum time (in theory).
Can't get you a copy though, sorry. Have a word with Boeing, they wrote the original.