Re: what kind of headwind should a sailboat be able to motor through?
If your engine won't turn more than 2300 rpm at full throttle you may be over propped, or at least have a dirty bottom. You should be able to get at least 2600 out of that engine.
My Yanmar two cylinder will rev about 2700 when conditions are right, i.e. clean bottom, smooth water, etc. That being said I don't think she would push me anywhere into 30 knot winds without falling off and getting some sail assistance, especially with a fierce chop.
The only time I've seen smoke out of my engine was when trying to get some more speed out of the boat when she had a fouled bottom (and propellor). Just had to throttle back and live with it until I cleaned her.
Sail Fast Live Slow
40' Norman Cross trimaran