Now Allen & Overy and Shearman & Sterling have completed the first-ever top-tier transatlantic merger, it is time for a few questions.

Behind the shiny communications façade, insiders will no doubt be wondering: can the A&O management really manage such a large U.S. operation from overseas? Was Shearman in such bad shape that the legacy U.K. firm is effectively catching a falling knife? Will the cultures gel?

A proper answer to these it could take years. The firm appears to have sought some early guidance by bringing in management consultants McKinsey for some expensive advice. But I'll give the firm this advice for free. Here are five things the firm and observers can watch out for in the coming year or so to determine whether or not this union is proving successful.