There is no doubt in my mind that a Sabre 65 cannot complete an around the world flight as depicted. My only question is why.
I do have a lot of experience in the Sabre 65, the best no-wind range one can expect in a 65 is about 2,300 nautical miles with a 45 minute VFR reserve. However, that is at long range cruise with step climbs to above 410 in the last couple of hours.
If you want speed about the best no-wind range is a a little over 1,500 nautical miles. That would be a Mach .82, or higher, cruise in the low 30's.
Having ISA or minus ISA OAT for climb out and at cruise altitudes will be critical for this trip.
Another Sabre 65 pilots expressed the affect of low temperatures on the 65 this way:
"When we first started flying the 65 it was in the summer. The 65 had okay performance, but nothing to write home about. Then our first trip with cold temperatures I thought that somebody had installed after-burners (re-heats) on the engines."
Anyway, sounds like an interesting trip and I wish them the best of luck.