I think you get into trouble when you drag in the MLC as a key caveat that obscures all the particulars. It's the particulars that matter: stressors, ego-integrity, and so on.
I can't, for example, point to a wealth of recent logitudinal studies that support the actual existence of what you are calling a midlife crisis.
I can, on the other hand, point to studies like Susan Krauss Whitbourne's and many others that directly contradict popular assumptions (popular among the general public, but not so much with research Psychologists) supporting the midlife crisis as common feathre of adult development. In fact, pshychologists commonly regard that diagnosis and model as 'not helpful'.
M-47,W-40,No kids D-filed 5/27/2010 Piecing - 10/21/2010 -=Soon to be banned=-