You can probably use a percentage of your "I" dimension (its around 12 feet) to figure out what size storm sails you need.
That being said, my boat has a 110% working jib that would probably be suitable for winds in the 20-25 knot range. (I haven't used it much on Lake Ontario)
This sail has a luff length of 30'-3" and an LP of 11'3".
I've also got a storm jib (again, never used, but probably good in the 25+ range). Luff length 20'2", LP of 6'7"
Hope this helps!
Mark 3, Hull #636