Brent: I've done it both ways.
With fish, no question, fresh is best. However, pheasants for me is now a no-brainer as they are much better after 4-5 days aging. I even age my ruffed grouse now (2-3 days in a refrigerator). As you mention, the Orvis cookbook (and even Rebecca Grey of Grey's Sporting Journal) argue for it in their respective cookbooks. I also performed a simple test last year to compare pan-frying grouse killed that same day with grouse that had been aged for a few days and it was no-contest. Both tenderness and flavor were greatly enhanced by aging.
Larger game animals are clearly different. Historically, I need to at-least partially process most animals in the field (deer/elk/antelope) in order to get them back to the truck (skinned & quartered) and...by the time I'm done with processing an animal the size of an elk, most of the meat has aged in the refrigerator for at least a few days anyway
This time I'm willing to try something different.
