I would argue that if the condition is "really long and boring", then it is *more* important to have braces and whitespace so it is easier to see where the actual action being taken is at a glance. The only one you mention that could work for me is:

do_something_useful()
    if really_long_and_boring_condition;
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Unfortunately, that's at the expense of putting the cart before the horse IMHO. The action doesn't matter if the condition is not satisfied.