Speedbrake will certainly work fine at 320 and is more effective at high speed you are quite right Flash and your way will work fine. However above 300 it does put quite a bit of extra stress on the tail although there is no longer any limitation on its use. Wouldn't go for 335 though as red line is at 340 and it doesn't take much to bump the speed up 10 kts and then its an ASR with engineering checks required. If I saw an F/O select 335 I'd tell him to back it off, in a pleasant way of course.
In an ideal world, ATC permitting, you would bring your speed back as you go high on profile so that when you get cleared to descend you can accelerate from slow speed, with or without brake, and dive more height off. VNAV does this for you with energy compensation but its not as dynamic as doing it for yourself. If its an airfield your familiar with you can even anticipate the problem and manage your speed and profile to minimise the problem. Of course at a-lot of fields this is usually not possable due to ATC restrictions.