The 90 degree turn is (as stated earlier) required when on NAT tracks, otherwise a 45 degree turn for one minute to get away from the airway is not a bad idea.(Todays navigation is deadly accurate). The other reason for doing so is to avoid negative G's when starting the descent. As for me I would descend at the Vb (rough air) speed since it gives the best protection from high and low speed buffet, and one never knows what the turbulence is like at lower altitudes. On the A-320 it's 275 kts which at m0.78 occures at 33,000 feet.

I agree with the 90 deg on NAT Tracks.

Some years ago I was taught to turn 60 deg off whilst conducting an emergency descent and our SOPs still refer to using the heading bug. But, I have never been able to find reference to this heading change in any manual. Seems to me a hangup from when we were flying along airways and turning 60 deg would get you quickly displaced from the centreline. Seems a bit irrelevant these days when direct ..... seems the more usual routing and the chances of someone being below you are minimal (unless someone can let me know otherwise). However, can see some merit in reducing negative G (or less positive G!), but also support the lots of things to do anyway and adding a requirment to disconnect the AP to get 45 deg AOB seems a little like leading to getting overloaded.

av8er, the 45 degrees I referred to is the turn from present heading, not the bank angle. The A/P remains "on".
Regards.

thermostat,
the 45 deg AOB reference was from a previous response, no offence.