Of the two an FJ is more driveable but they're similar and both doable. Every driving/comfort complaint you'll have about the FJ you'll have moreso about the BJ - they're louder, slower, hotter, smellier.
A BJ40/42 is unhappy at any speed over 55mph. If there is a hill or headwind then plan on 50mph or less.
A 5 speed would help keep the revs down; the high end late models were available with those. But you'll still be pushing near to 1200F EGTs if you try to run a BJ42 at 65mph.
A turbo is another good option (though I've found those tend to move heat from the EGT to the coolant, for better or worse). A BJ42 with a turbo, IMO, is about on part with an FJ40 in terms of driveability.
The BJs win for carefree keep-on-ticking-ness though, IMO. Gas mileage too.