I always pay the extra for overnight, and if the fish are large, prefer airport to airport, which means they get there in a matter of only a few hours.
I also find airport to airport competitive with price.
The last time I did a combined order with a friend, the weight was way up there (3 boxes total, almost 80 lbs), but the price was only slightly more than a UPS 5 lb box.
Of course you need a close airport that is a Hub that can be used, and you must pick up the packages at the airport yourself.
But this to me is better than letting the boxes bang around in a hot or freezing truck half the day.
Even when shipping with the US postal service within 24 hours, I call them first in the morning arrival day, take a vacation day off work, and arrange to pick it up myself at the post office myself.