Ted Brewer has written on the concept of a "50/50" motorsailer that has decent sailing characteristics, but can become a "trawler in being" if desired. We own a motorsailer, but it has a relatively small engine (52 HP pushing 25,000 lbs. light load) and can make 4.4 knots reaching in 9 knots of wind.
However, I will allow that it's got very generous stowage below and has a pretty stumpy sail plan for a modern boat. The sail plan is conservative, rather than stumpy, however, in the sense of heavy air or steady trades. In 20 knots, she'll go as fast as most boats, but with a kinder motion. Close-hauled in light airs? Not so much, but not as hopeless as I had thought, either.
We intend on sailing her as much as we can. We also intend on expanding our fuel capacity from 100 to 140 gallons. The idea is the option of having a greater range, plus the option to actually motor-*sail* (to go six knots when really the wind would only produce 4.5 to push the boat) for extended periods. This, of course, keeps the engine under load and the batteries charged, but means the diesel is in "sip" mode as we might just be running at 1500-1600 RPM or so instead of the 2,200-2,400 needed to do six knots with no sail assist.
We are also investing in a feathering sail and likely a light air genoa or Code Zero to change as needed with the existing Yankee-cut jib. So while we are leaning toward the "sail" part of the equation for the reasons that a) it's cheaper, b) it's quieter, c) we aren't going to be in such a hurry that 4 knots under sail will often fail to trump 6 knots under motor, we are under no illusions that we'll match J-Boat performance. But we will go, and we will get home, and a "lightish" motorsailer seemed to meet our requirements, which include the ability to circumnavigate and to be handled by an Ellen MacArthur-sized co-captain when it's her watch.
Not to mention that having a pilothouse plus a second deck steering station seems like we're getting an extra 50% of a boat.
But our pilothouse windows (1/2" thick through-bolted Lexan) will require storm shutters, and that will require some thought!