Good question indeed!
Heaving to we've so far only done in moderate conditions in order to do some
exterior plumbing (blocked toilet). That worked very well, although as a storm tactic I'm not so sure.
Down the Atlantic coast of Spain and Portugal last year, we often sailed in 3-4m waves, but those were long interval Atlantic rollers, they're fairly pleasant and never caused us concern, except when we once got a fountain up the sink in the heads as one slammed into the side of the boat just right. We learnt to close the sink seacocks that day
This year we got caught out in a gale (top gust 47 knots, 40+ sustained, ~3m seas) on the way to Almerimar (a blog article I've yet to write). We ended up motoring upwind to get to Almerimar, as the downwind port was too shallow and open to the swell, so unsafe to enter in these conditions. Unlike the Atlantic, the Med (due to higher salinity) kicks up incredibly quickly and with a very short and steep sea that is much more dangerous. The rough seas made progress very slow (~3 knots at throttle wide open - and the 40 Ocean doesn't suffer from an undersized engine) and I had to hand steer. Each wave needed to be negotiated individually or else the boat would fall down the trough with a frightening bang that shook the rig (happened a few times when my sunglasses were too encrusted with salt to see). I ate a lot of saltwater coming over the sprayhood. Big waves had to be taken at an angle of around 20°, not head on. The boat did well, but in hindsight it would've probably been smarter to turn around and run off, although that would've seen us in the crappy weather for much, much longer, it would likely have been a much better ride. The companionway sliding hatch needs an exterior locking bolt, something I shall add this winter - after some saltwater lubricated the tracks, it kept sliding open. The bow dipped in and scooped waves that would run across the deck and we had to block the rope gates under the windscreen with towels to prevent water coming in the cockpit that way. Not dangerous, but annoying. Not sure how to stop that. The Dorade vent on the foredeck also got overwhelmed - it can be closed from the inside, but nobody remembered to
It's always the seas that cause the problems, never the wind itself (unless perhaps it gets much higher, say over 60 knots). We had some fairly squally weather since Sardinia in the last month, and a few of these squalls had more than 35 knots wind, but they didn't last long enough to kick up big seas, so we just reefed a bit when we saw one coming and barreled along at 8 knots boat speed under autopilot while hiding under the sprayhood from the driving rain. The boat really enjoys this, especially on a beam reach (which unfortunately means the rain comes in sideways).
Another time, in not quite as bad weather as the Almerimar bit, we ran downwind under reefed Genoa and it was hugely more comfortable and far less strain on the boat. I think I'd vastly prefer that, as you also get the benefit of reduced apparent wind. Waves on the transom were no problem, it's plenty tall and we never got the vents under water, although I would like to fit some close-able vent covers there instead of the louvered ones the boat came with. If the boat started surfing (not likely in the Med, but possible in longer Atlantic swell), I'd try trailing mooring lines as suggested in
Heavy Weather Sailing, or if I were doing this a lot, get a series drogue. The book (which I'd recommend reading) does not speak too highly of conventional drogues, as they are ineffective if the single cone gets in the fast flow of a wave - it will do nothing to slow the boat down then, and constantly adjusting the line length is impractical. Retrieval of drogues can be a big problem though, and at a time where the crew will likely already be exhausted.
Sea anchors are much larger, they effectively stop the boat relative to the water, holding the bow into the waves, which creates enormous loads on the attachment points. I don't think they would stand up to it as factory fitted, especially the non-Ocean ones.
Lying ahull is a terrible idea in any boat and likely to get you rolled and lose the rig in a storm. The book goes into some detail about that and leaves no doubt about this.
A tactic you didn't mention, but is widely used (in the book, and we've done it as above), is motoring. This worked well for us at around 20-30° into the waves.
We do have a storm staysail on a removable stay that the original owner had paid a fortune for to have fitted. I've not yet figured out how to use the thing in practice, as in conditions where I'd want to use it, I would not go on the foredeck willingly to set it up. Perhaps leave it rigged for ocean passages where the interference with tacking would be less of an issue.
Another key consideration, especially when well offshore is exhaustion. Any approach where you do not have to hand steer is preferable for short-handed crews. Manual helming requires concentration and in big seas serious physical effort. If you lose attention for one second, you can roll the boat. So anything that lets you use the autopilot safely is far preferably. For our boat that is again running downwind. This depends on your autopilot type - modern ones all have gyroscopes and should fare well with this. Older ones with just a fluxgate compass would react too slowly. We upgraded our older Type 300 with an optional gyro, which definitely helped it steer straight in rough seas.
