Standard MGB rear gears at 3.9, and there isn't a lot of direct swap options available....MGC had a couple different ratio options, but MGCs are scarce so those are not easy to come by. Hence the electronic O/D transmission is a coveted option and popular swap. Some people swap to Toyota 5-speeds as well, but that's not my thing....The factory MGB gearbox is actually a pleasure to use.
At the end of the day, we're not used to spinning 3500-4000RPM on the highway, but that's what these cars and engines were designed to do, and they'll do it happily for many, many miles. It's just not terribly enjoyable, for me at least.
MGB does drive very similar to the NA Miata though - back when The Hire had his NA I drove it a fair bit and the Miata does feel like the natural evolution of the MGB.