Chromogenic films will gain contrast with extended development same as "normal" films; they won't gain shadow density other than the slight amount that results from a steeper gradient.(posted 8333 days ago)For "normal" films you have the advantage of using a "speed-increasing" developer, usually a PQ developer such as Microphen or DD-X; these will give usually a 1/3 to 2/3 stop increase in real speed based on shadow density compared to an ordinary MQ developer. Think about it this way; HP5+ developed in Microphen becomes an EI 640 film with normal contrast development and you can push it from there.