If you are seriously looking in to good IP tuning with larger elements go for the original 6mm elements out of the 606 IP or better wait for the 7.5 mm elements.
I am trying to find s.o. with contacts to a good bench shop to be able to swap elements and do the (intelligent) adjustment in the US (there is already a potential possibility). External full load adjustment is not magic, I made it for my MW IP.
In my opinion this should be the way to go. Just shipping elements from Germany to the US not IPs twice.

Tom