One option I considered when i swapped out the panel at my wife's grandma's was to get a Piece of 4" ductway (+ end caps) - have all the runs terminate in there, nipple the ductway to the top of the new panel, and then make the appropriate (extended) runs using THHN/THWN to the new breakers.
It's bigger visually, but "cleaner" (less "loose" pipes and cable to the customer)
