We used 30, I found myself rarely adjusting the speeds for my own preference (Iworked for that Irish airline).
I did what needed to be done, for example If i knew the easyjet ten miles ahead was going to the same airport as us then I would overtake. This was not too difficult as those chaps often cruised at .76 and once .74!
I tried to beat the traffic at the end of the night which often worked and enabled ATC to give me us the fab shortcut which saved approximately 600 to almost 1000kgs!
So to answer fly the company CI and adjust your technique appropriately for the given circumstances.
De Facto - You have a brain - use it. You don't have to stick rigidly to SOP's, you are deliberatley reducing your choices unreasonably.