For me it is a 300 Win because it is rare (never) that there is not at least the possibility of seeing something besides a deer that needs shot at, might be a coyote or wolf at extended range, could be a grizzly or black bear that has a bad attitude and lord knows with all those sasquatch out there running around a potent weapon is certainly in order any time one takes to the field. The biggest reason is that most times I am hunting deer I have an elk tag in my pocket too. If I ever start hunting in a place with no bears, lions, wolves, elk or sasquatch I may consider something else, but I doubt it... I know OP said elk was not part of the conversation but out here it is hard to talk deer hunting without mentioning elk and sasquatch, anyway the 300 gets the nod for me based on versatility...
Better to do it when you're young so you can talk about it when you're too old than talk about it when you're young and do it when you're too old.
