I like the way The Ipcress File combines the film noir feel you mentioned with a kind of absurdist black comedy. This applies even more to the second film in the series, Funeral in Berlin. And Michael Caine manages to be extremely cool, and rather dorky, both at the same time. I think it's the finest acting he ever did, because it's precisely what the film requires and allows the film noir/black comedy mix to work so well. It meshes perfectly with Guy Doleman's marvellous performance as Colonel Ross.