Hi
I used to be a high protein guy koi food wise but it all depends on what you are trying to achieve and what temps you are feeding at and the quality (genetics) of the koi / carp on how well they will grow .
To high a protein level in koi food at average pond temps (unheated) imho is a waste of time , it just puts extra demand on your filters as the un processed protein just gets cacked out by the koi . I would far sooner feed a lower protein level food more often through the day and the koi be able to utilise the food by feed little and often .
I,ve been useing the Orchard Fisheries koi premium pellets which is 40 % protein with good results and very little waste and you can feed all year round with this food , but everyone will have there own favourite so you will get many different replies 
It also depends on wether you are feeding these fish with other larger koi / carp in the main pond or trying to grow them on further at higher temps in there own bigger tank .
EDIT…
Sorry just read they are going in your pond , so the Orchard Fisheries koi premium would be my choice as a all year round food but as said everyone will have there own choice 