Totally different cars despite being the same dimensions, weight, displacement, etc. Miata has power steering, perfect weight distribution, 4 power disc brakes, modern independent suspension and handles effortlessly without losing one's feel for the road. Almost no one can stay with me in a cloverleaf. The grip is uncanny. Seats hold you solidly in place. MGB with no power steering or brakes, live rear axle, alot more body roll, flat seats, high profile tires, and big banjo steering wheel takes more muscle to drive.
I love them both, but they are very different from one another.