Brainstormin' 440 vs 5.9 ...

I think the 440 that you are planning will be slightly faster than the 5.9. I DONT think the difference will be worth the time and money and work invested in making the swap.
With some more compression, and some better heads, then I would make the swap, but I think the 440 would have to be modded a bit more than you are planning, to make a significant difference.
Your 5.9 runs real well, for what it is!

Edit: imo, the torque advantage I would expect from the 440 over the 5.9, will not show up on the strip, because of the 4.30 gear. If you were running a 3.23, I would be more confident in the 440 being faster than the 5.9.