Descent speed Policy for the 777

As most NGX experts have learned, it was best to have the NGX descent speed to be .78/280 kts on the FMC Descent page.  I think ATC has most jet traffic descend at that speed until the transition to 250kts at 10,000ft.   I don't know the specific reason, or if it's only applicable to aircraft in the 737 class, but what would be a reasonable speed for the 777?  IIRC, the MD-11 had a descent policy speed, I think the default was 290kts, and whatever the mach cruise speed was at cruise until FL280 or whatever FL that mach changes to IAS. 

What do the pros use for a descent speed on the 777?   I've been using the mach cruise/280 kts, but it seems a little slow.   But I also remember seeing some STARs in the U.S. instructing traffic to be at 280kts or slower at the intermediate altitudes.