The case for going 400 block-For the cost of switching intakes, pushrods and adding a distributor spacer, you gain a huge advantage in strength ,bob weight, and some over all weight reduction. Changing rear gears to cross at 6,000 rpm would be a good move with a 500 cube motor, and the package ought to live an extremely long life, with shift points at somewhere around 5500 rpm. The gear change should bring the launch torque back down to where it was with the 440, but the converter will flash higher and be more consistent if the track gets iffy. Your shift points will be further down track, allowing for a tad more consistency which might be worth as much as .01 or so in consistency. My experience was when I went to an air shifter, and my ETs narrowed up .02 average, running in the nines.
I vote for a rear gear change,and a 400B 499 cube package.
The rear gear you currently run is probably slowing you down, or at the least just way over revving the motor. No matter what you decide, you can definitely drop the rpm to 5800 to 6200 rpm in the traps (depending on short block size)with the 590 cam and not lose much if any performance.