are #5 heads better than #7 heads.

 

To a large extent, 6 of 1 to half a dozen of the other. 7’s have hardened exhaust seats with rotators on the exh valves in stock form . AFAIK they are dimensionally the same in the ports and chambers.
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^^^THIS. Note that the "hardened" seats are not inserts but just induction hardening of the parent metal cast iron. This hardening is very shallow and pretty much gets removed the first time you cut the valve seats, so that really isn't a discriminator. The rotators mean that the #7 heads have deep spring pockets on the exhaust side, which will require shims under the springs if you plan to delete the rotators to reduce valvetrain mass.