What is the difference between a v6 and a v8 engine that have the same horsepower?

okay say you have a 1968 mustang with the small 289 v8 engine that has about 200hp and you have a newer 05-09 model mustang v6 engine which makes about the same power. is one more powerful or better in any way than the other because one has more cylinders? i've just been wondering about this for awhile.