Starting easy is always good for marathons!
Within reason. My London 2000 went 7:30 6:15 (panic) 5:15 5:20 5:30... and did not end well. But I guess you have chip time to run to.
If it is chip time then there is no hurry to get over the start line. Why not drop off the back and wait until there is room to run ? Then race at the pace that you want to from teh start line. This gives maximum positive psychology later in the race as you start to pass people who wen toff too hard.
Not being able to run freely because of massive numbers of people is annoying and wastes energy