Different powders respond differently to the cold. There are good temperature stable powders. Also many lubes do not gunk up your action and are not overly temperature sensitive (Breakfree CLP). WD40 has no place here and will always gunk up.

As to the 150 grain bullet recommendation sectional density and bullet construction are more important than weight (though weight is a part of the SD equation). For any given expansion more sectional density is required to achieve the same penetration. 

Whatever you shoot shoot heavy for caliber with a bullet constructed to suit the task at hand.

As to cleaning solvents Shooters Choice Lead Remover and Bore Tech Eliminator and CU2+ are very good choices that I highly recommend.