There seems to be some confusion about takeoff minimums vs. requirements for a takeoff alternate. Neither of the two arguments in the original post would change the takeoff minimums, as the ability to return to the field is a concern when determining if a takeoff alternate is necessary.
Unless equipped with an approved guidance system, RVR 5/5/5 is the lowest I've seen. An HGS will get you RVR 3/3/3 at a few airports.
Last edited by Dash8Pilot; 02-02-2008 at 04:23 PM.
Reason: clarity