Big Block Strokers - How big should we go?

It depends on what you want... you're trapping at 6500 and IMO the SRs will not support a bigger engine at that rpm. If this is a place holder - smaller would be better IMO. B wedge 470 or 451. If you are looking to invest in a real block and go from there I'd recommend a change in approach: Plan to re-gear (4.10-4.30s) and re-converotor and build the biggest you can afford. Plan to sell the top end (or place holder) and invest in something that has more ability like the -13s or B1s. the thought being as a bracket truck you want consistency and less maintenance and a big rpm engine just needs more and is less likely to be consistent in mixed weather. Might even want to consider E85 or methanol for it.

Edit for the entire top end re-use - another 440 would mean no new intake needed.