The straps on the Super C Audax are very long, so that you can heap stuff up under the drawstring bit (operculum?) inside, fasten the buckles and then snug it down tight. Not too sure about using the buckles with cold fingers, though - on my Lowsaddle Longflap I don't bother threading the straps through the exit side of the buckle** and it's pretty easy to use with cold hands. When I'm cold I have to fumble a bit with the Super C buckles to feel which bits are squeezable.
**several folk on PBP told me that my straps were awry, including one courteous gentleman who said haltingly "excuse me sir, but your briefcase is not correctly locked".