I wouldn't say the performance is the same, it is just that you can go plenty fast with manifolds. It is rather easy (given the resources) to build a car that looks fairly stock yet has the ability to run 11.50 at the strip.

If you aren't going to put a roll bar in the car then you run the manifolds. There really shouldn't be too much of a problem of getting a big block with manifolds deep into the 11's.