I am no expert but I'll share my observations:
Start by going sailing in heavy air for an afternoon and play around with different sail combinations and different points of sail. Don't forget to try heaving-to as well, so that you know what is necessary for this manoeuver to be stable with different sail arrangements.
From a practical viewpoint, tri-sails are often left rigged on the mast ready to go. This means more clutter on the mast, more fittings and ropes and the like, and more weight and windage on deck. The compromise of a small heavy main instead of a tri-sail makes great sense because no additional hardware is required. *BUT*, it requires changing the mainsail entirely in a lumpy sea and strong winds.
The mainsail on our boats is small to begin with, and I find that I skip the first reef and go right to the second when reefing. Perhaps others have more experience using a single reef. If two reefs in the main and a storm jib are too much sail then I would be thinking about taking down the main or the jib (or both) entirely. There is a surprising amount of windage just from the furled main and its cover --
Were I buying sails today I would buy a main with two reefs, but make them deeper (taller?). The effect would be a third reef but would not require me to fit extra reefing hardware. This option seems preferable to a tri-sail because it means less to deal with. Alternatively, I could just go with three reefs and only set up jiffy reefing for two and keep the third reef point as an option. I acknowledge that making the upper part of the sail strong enough for a blow may hurt its light-air performance.
Think about your headsails and how you will manage them in rising winds. They are a complication that you will have to face more often than you will need the tri-sail.
Finally, the best argument against a tri-sail is that it leaves your budget intact so that you have more money to put towards self-steering. For cruising of any distance, self-steering is THE best money you can spend (I like the Cape Horn myself). One could put up second hand rags from a different boat and the Contessa will still go forward. Self-steering is like having a reliable and well paid helmsman with you 24/7, rain or shine.
Thanks for the great question. More entertaining than work!