Do you know for sure what size the bores would clean up at?
Has the block been sonic checked (which may be paranoia, but I always do it just to know) ?
More stroke will of course build more low-mid torque, all else being equal.
I would think a 505 would use more fuel than a 440, all else being equal, but I have no personal data on that.
That said, 440CI moves even an Imperial along pretty well on the highway.
So you might not want/need to reinvent the wheel, so to speak, let your wallet decide the sleeve/piston issue.
If that trans is a 30% reduction in RPM, that amount of OD on my 5500-5800 lb Dually (depending on what's in the bed) is worth 2-3 MPG.