Excellent post Will and for the first time in ages it's a distinct pleasure to agree with 411A - that's the way I see the rules - utilize the regulations as promulgated by the licensing authority but if the country you're opearting in has more restrictive criteria you'd be well advised to adide by them. For example, the basic Part 91 (as I see it) has no specific reference to take-off mimimum RVR's but if you were to wizz off the runway and clobber the G/S antenna (or even a light) in zero-zero you'd be in a bit of trouble.