[Runequest] Shield & armor questions

[royce at efn.org]

Greetings,
   If I may impose on the expertise and experience of my fellow RQ'ers, I
have two questions.
   First question:  In RQ 3, the Viking Round shield seems a poor choice
-- if I base my decision on armor points to encumberance ratio.
   (The Viking Round shield has 10 AP, but an encumberance of 4.  The
buckler has 8 AP and ENC = 1; the Heater/Target has 12 AP and ENC = 3.)
   Is this a good basis for judging the merits of the shields?  If so,
then why would anyone choose such a shield?  If it is not a good basis
for judging merit, then why not?

   Second question:  In RQ 3, chainmail offers 7 AP, while platemail
offers 8 AP.  Only a 1-point difference.  A lot of money and
encumberance to gain that 1 point of additional protection.
   Do you agree with this?  If so, why?  If not, then what might you
suggest for a house rule?

   Many thanks ahead of time for any answers, insights, etc.
   Sincerely,
Asher