That would be a great objective but with one caveat, for twin-jibs, not a spinnaker. I don't know of a boat that doesn't require some active trimming of the spinnaker in 25k+ of wind, especially in anything other than flat water. To have an AP handle a spinnaker in breeze with no intervention requires a much reduced spinnaker size or more preferably a spin with a bolt-rope luff to keep from collapsing which is what all those RTW boats use.
Depends on the boat... a Cal 40 has a short rig and longish keel (ie it resists rapid turns) and with a decent autopilot will go all day and night in 25k with the chute up (and a quartering sea). Being able to sleep in these conditions is the hardest part. Now when it gets much above 25k of wind... yes a shy kite will keep the AP working... at 28k its time to drop the chute (at least with a moderate cost AP setup on a stable boat). Now how those southern ocean racers keep chutes up in the 30K+ range... god only knows.