The Ilford chart you mention is what I have used in the past with terrible results, and from what I understand I am not the only one. In addition it only goes to 30 seconds exposure. I am guessing the place I want to photographs will have soemthing in the 2 minute range for which I will have to compensate for reciprocity. While I am sure that FP4 and FP4+ would probably behave very similar at these exposures, when you are doing 12x20 it pays to be as accurate as you can...