Exposed Arista Premium 400 at ISO 64, how best to develop it?

I thought I had one of my last rolls of Kodachrome 64 loaded in my camera but upon rewinding it and removing it from my camera, I discovered a roll of Arista Premium 400 instead. Certainly one of those "duh" moments.

I have both D-76 and HC-110 developers. The Massive Dev Chart only lists an ISO 50 recipe for Kodak Tri-X 400 in D-76, but nothing for HC-110 and, more importantly, nothing for ISO 64. What's my best bet for developing this roll?

I'm going to guess and see if anyone else agrees: reduce normal development by 20-25%, gentle agitation.

HC-110 1+100. 72 degrees. 9min. 1st min then 10 sec of agitation per min.

Ballpark.

The ISO 50 time should be fine. Well as long as it actually is good for ISO 50.

Thanks for the tips!

Would I gain anything by using HC-110 over D-76 in this scenario? I suppose that having exposed the film at ISO 64, it'll be less grainy than usual?