best glide speed of a warrior

the best glide speed of a warrior is quoted as 73 kts. but best glide should
be at best lift /drag ratio which I recall is at about 4 degree angle of
attack. But this must be a function of weight. So my questions are what
weight is the 73 kts based on ? and how much does this best speed change say
between maximum weight and minimum wight , or lets just say an 80 kg ( 176
pounds for the folks up over ) pilot flying solo with half fuel? Why ? I
am just curious, I like practicising my forced landings ( solo) and just
wondered how much extra time /distance i might get by flying at a more
"correct" speed. My flying school actually rounds it off to 75kts,
regardless of weight.
Terry