360 header gains?

360 bored .030 over, eq magnum heads slightly ported, edelbrock rpm airgap slightly ported, 10.7:1 compression .
Cam: 109 lsa
Duration @.050 239 242
Lift .562 .559
Currently have hooker headers 1 5/8 primary 3.0 collector.
Currently makes 440 hp 490ftlbs

Exhaust is 2.5. To rear diff exhaust is pretty good. Over the axle not so much. It is crushed bent. Some spots are crushed to 2 1/8. Instead of redoing it I am thinking of putting an x pipe in so each cylinder can take advantage of both pipes. Any estimate on how much the x pipe would gain? Read x pipes gain between 7-12 hp

Also thinking of getting 1 5/8 - 1 7/8 tti step headers any advantage of this over the hooker headers?