Issuing an *immediate* distress call would depend on whether anyone can actually help you there and then, I'd have thought. If there's spare capacity, fine, but if the pilot(s) are working 110% to keep the aircraft from doing something terminal then waiting for a reduction in the workload might be prudent. Even with things such as emergency descents and Atlantic turnbacks, the priority is aircraft control, followed by communication.
I've been witness to some extremely pedantic discussions over the use of PAN over MAYDAY and vice-versa. At the end of the day, who gives a **** as you can always change your mind about your status later. Unless I was operating in central Europe, I'd use the M-words every time as the other option is often not understood and/or leads to an extended conversation.
I agree that in English speaking countries, yelling "Help! Help! We're on fire!" or whatever would have the desired effect but in places where the mother tongue is radically different, this may lead to a large question mark (or whatever punctuation they use) appearing over the head of whoever you're speaking to and possibly no action taken.