I don't think McCluskey had enough time to process what was truly going on in front of him. He saw it, obviously. In the novel, Puzo described McCluskey looking at Michael like "now what the hell did you do that for? - hand over your gun and surrender."

I think Sollozzo was naturally wary, but not overly concerned about Michael. He vastly underestimated Michael, which was to the Corleone's favor. As Michael stated in the novel, once anyone makes up his mind to kill somebody, that is the toughest part - reaching such a decision. Sollozzo didn't think that Michael had reached that point, which means Michael did a great job of concealing his true emotions. This was one of his father's great traits and something that Sonny, quite obviously, could not do.