Often the reason is possible valve to piston clearance. The position of the piston in the bore and the valves
You do not always need more or even the same amount of exhaust duration or valve lift to get the job done.
Dwayne did my W5 cam. It was 699/672 on exhaust. Car ran great. Every combo is different.
I had no valve relief issues. Most quality Pistons have plenty of room
