From my 'working viewpoint' I would not wish to see you turn 90 degrees left or right, and I guess from your viewpoint, if it's an emergency descent, the last thing you want to be worrying about is making a turn!!!
7700 is 'the best' thing that you can do ASAP as it alerts everybody sitting in front on a radar that you have a problem. More importantly, if 7700 is seen coupled with a quick descent, we will do everything to get those beneath you out of the way, which takes me back to point 1. I you're just descending in a straight line, that makes track projection and the 'clearing of a path' far easier, if you start turning however.......
As an aside, if faced with such a scenario, it would of course be nice to know that you are able to make turns, as this would make it easier to ensure your safety on the way down.