If you want sustained highway speeds, its not just the motor you need to look at.

I had 33s and running a weber. It would hold 80mph just fine for long trips. Only problem were steep highway climbs. So I did the turbo swap and have 4.875s waiting to go in.

What tires and gearing you run can play a big role in highway speeds.

88 Montero, StarQuest turbo, Kormex 5speed +tuff-pan w/phoenix f. stage2 clutch, 4in lift+33' tires, 4.875 lsd, short-throw shifter, Aisin hubs, SR big brakes, gen2 uca's, elantra alt, and so much more... 16g turbo w/hardpipes + 4.90 locking disk-brake axle soon (maybe lsd or aussie front??)