I feel your pain. I went through this debate with myself for several months before I settled on D60s.
I did have a HP D44 for awhile and the Friday before the weekend I was goning to tear it apart I came across the '87 and '79 D60 axles.
I played the “juggle a bunch of axles at my parents house” game. :laugh: I literally went through a set of XJ 30 and 44 axles, a ’78 F250 HP D44, a ’87 F350 HPD60, then settling on a pair of D60s out of a ’79 F350. All said and done after the swaps I ended up with the ’79 F350 axles for next to nothing.
What settled it for me was the fact I knew I had another DD and that my XJ was a trail rig so building 44s only to go 60s later didn't seem wise. However, if it was my only DD, I'd rock the 30/44 combo (like you've got) for awhile longer until you need something bigger. Then I'd go D60s or a 60/14b.
Yet, how is the 44 you found built? That might throw anyother wave into the pool.
I would agree with razdrvr that a 609 when comparing it to junkyard/second/third hand 44s and 60s is a COMPLETLY different level of banking and paychecks needed. :laugh: