The magic number, here, is 75%. You want your exhaust port to flow @ 75% of your intake port. Most stock heads (especially BB mopars) don't do this, so cam manufacturers figured they can compensate for the heads shortcomings by extending the duration on the exhaust side.

What has happened now, is that split pattern cams have just become the norm, and the general public percieves they are getting a better engineered product with varying #'s on the card (not really knowing why)

Most good aftermarket heads do support the 75% number, however.

The key when choosing a cam is knowing what your heads will flow, and complimenting that curve with the cam. With good heads that flow properly, there is a strong case to be made that you'll maximize the power available from a given duration and lift spec. with a square pattern cam. Your intake, carburetor, and header selection also plays a role here.

I conferred with Member, Jeff Patterson, when choosing my cam, and we both agreed that my combo seemed to call for a square pattern cam, so that's what we dialed up from Engle.