there's a guy that has a massive pond that has em mixed, the Tk guy he's talkin about
as far as koi not liking warm water they can definitely handle it to some extent, some mexican let a koi loose in a pond that i fish somethin like 3 years ago and that son of a gun is a solid 2ft+
dude carp will live in anything i found most of our cold water natives over in aus like murray cod etc can live in 30 degreed c anyway so a calp would love it!!!!!