I' sure that on a maximum effort project a header is worthwhile.
However:
You're throwing away quite a bit of heat energy from the far greater radiant wall surface of the headers (as opposed to cast-iron manifolds).
The cross-over shown in the Dragula photo is IMHO too big (looks like 3"?), keeping the velocity up is always important. 1,000 HP LSX motors use the original truck manifolds with 2-1/2" outlet and 2-1/2" cross-over tube. Big primaries, big collectors and big cross-overs delay spooling a lot, without significant increase in maximum boost.
IMHO the single most important advantage for a header isn't RPM-tuned scavenging, or reduced back-pressure, it's keeping the individual pulses at the port separated for as long as possible, but a tri-Y does that just as well, and smaller, lighter, cheaper.