+10 Shield[0]
It'd do more damage than a +4 Sacred mission or +4 stone buckler. ; )
But out of those two, stone buckler because it has a slot.
Sheild chain damage does not improve after +6 on any refined sheild.
Sacred Mission, on this server at lest is not heavier than the stone bukler your info was probebly from roempire or rate myserver, I saw a scared mission selling some months ago and it was alot lighter than the buckler.
If you want good sheild chain/bomerange/push damage then use a stone buckler, I also recomend a HHHP weapon or TTHP weapon for max damage cause sheild chain if effected by +% cards (but not by + attack cards) also str helps it to.