I just checked the original (VandeStadt) designer's drawing for my boat. It is an IOR 40' "one tonner", with a racing
rig (i.e tall mast
, big sails). The mainsail is a little over 500 square feet.
The trisail is 20% of the mainsail area.
If I were in your shoes, I would go for the smaller trisail (i.e the 22%).
Assuming you have decent reefing on your main, you aren't going to be pulling up your trisail until conditions are so ugly that you are pretty much in "survival" mode, so smaller sail area is probably better than bigger. I have carried a storm jib
and 2 reefs
in sustained 40-45knots true wind
an the boat felt comfortable. I probably wouldn't go to trisail until the breeze was sustained 50+ (your mileage may vary, of course).
Bear in mind that you are really only looking for balance & steerage with your storm sails
up. too little canvas
is not going to be a problem in this case, whereas too much will definately be a problem.