3/16 or 5/32 lower shrouds?

[Brion Toss]

Hello,
The upper shrouds on your boat take about 45% of the total shroud load; the lowers share the remainder. So if you have 2 lower shrouds per side, each will take about 30% or so of the total load, once you allow for the load to shift a bit between lowers under way. Therefore the lowers should be smaller than the uppers, and increasing them will make tuning harder, not easier, plus the larger wire and fittings are costlier and heavier than necessary. So if your uppers are the right size -- and that is another subject -- then your lowers are, too.
By the way, your backstay should be smaller than the jibstay, for reasons that will be revealed when I finally get around to posting the winner to this month's Puzzler.
Fair leads,
Brion Toss