Max K-1 to D2 ratio?

[zuiko]

Well winter is coming and I need to get some winter fuel before I get all gelled up. I know I have bought stuff at the pump that was supposedly 60/40 (60 being the kerosene) and I think they run higher mixes in the arctic. I'm thinking I might just buy my own kerosene so I have a better idea what I am getting. Is straight K-1 OK for winter use (-30F to +40F) so long as I use an additive like howes? If not what is the max concentration? Also.. is there actually any difference between K-1 and D1? Most stuff I have seen says there is not any difference between those two products aside from maybe additives and taxes.