Thanks to all for the info. Lots to consider here. I've got some time to figure this out, as our air temps have dropped like a rock in the past couple of days. Water temps still at 72+, but may end up in the 68 range before this cold snap is over.
Currently have a large group of jd's breeding in another small pond, and recently lost an old friend orange midas, 10+ years old. I think going mellower would be my best bet, but the allure of a temensis or dovii is too much to rule out. Could either of these be paired in a 300gal? Or is that just not enough space for more than one? Are there likely to be compatability issues with the marble cat with these brutes, since he is definitely staying.
Severum Guy - have never kept severums before. How are they for visibility from above? Some of the wild type individuals on Rapps site are just amazing looking, but will I ever see them?
Thanks again everybody for all your insight.