A minor point...when comparing armors, you should not suggest to add a ritual in to make something comparable to a +5 mithral FP. You can add a ritual to a +5 mithr FP to effectively make it +6. As the ritual can be done on ALL of the armors, it should not be brought up in comparing. A +4 armor will always be 1 short of a +5 armor...
Sorry, no big deal, but that was bugging me...