Calculating Encumbrance for non-weapons

So my mage wants to do Leap of Homecoming with a sack full of silver coins. We are using the Transforming Mythic Europe pg 107 rule, "If the target is burdened by an unusually large load then casting requisites are certainly justified. As a guideline, any Burden which causes an Encumbrance of 3 or more should require a requisite appropriate to the material comprising the majority of the weight:"

Sounds straightforward except I cannot find anything that equates weight to load or encumbrance. How many pounds of silver equates to an Encumbrance of 3 or a Load of 6?

42 pounds according to Grogs, "Encumbrance and Load", page 47. Which starts by saying that weight and encumbrance are purposefully abstract, so feel free to adjust it.

If I read the rule correctly, Emcumberance is the total Load transformated to Burden exceeding the Str.
So, If your magus is strong enought, he can Leap with more on him without requisit.

Since 6 Load cause a Burden of 3 (calculation from 0), I guess any materials of load 6 or more when the character is Encumbered at least for 3 trigger the need to a Requisit (a magus with 4 in Str could wear a full mail (Load 6) and a greatsword (Load 2) without a requisit).
That is, if the rule are correct and you only have to check for Encumberance when deciding requisit.

As for the real weight :

Full chainmail is 6 load. It is between 20 and 30kg (depends on what "full" means)
Greatsword is 2 Load. It is 1.5kg (for a non-ceremonial two-handed sword)

BUT you have to take into account that these objects are particularily suited to be worn : the weight of a full chainmail, despite being high, is supported by many parts of the body. Greatsword are balanced etc...
A pile of gold coin are not balanced nor pratical at all (maybe if you have a crafty thief magus with a lots of pouch, you can change this statement )
So I would divide by 2 or 3 the absolut weight for factual weight :
10-15kg of coin (divide by 2) or 7-10kg of coin (divide by 3) for a Load 6.

Anyone familiar with long walk, trek, or usage of infantry equipment will, I think, vouch that repartition of weight can change how a long day of hiking feel. If your muscle do less effort, well, your magic must do less to