I fully agree with PGA, the fact RVR can be replaced by pilot assessment has nothing to do with the "90m visual segment from the cockpit". But the pilot can assess the RVR himself and has to make sure it is above his requirement (125m or whatever...).
About the stop end RVR, you wouldn't always calculate your ASDA in relation to the stop end RVR, but if you take off with a light turboprop on a 4km runway i don't think it's relevant