Stanadyne, as it's one of the few (only ?) that has OEM endorsements. Hard to find though. It's advertised to provide as much as a 40 degree lowering of the gel point, and considering that #2 seems to have advertised gel point of around 0 degrees (?), it seems to agree with observations of some that even with Stanadyne they started having problems below -40 F. For lower temps you evidently need to start mixing more #1 fuel.