So I think it depends on what you need, vs what you want.

For instance, is it normally during cold months or hot months you lose power for that length of time.

do you have to have a/c or heat running? portable small a/c or fire place to heat instead?

just powering a fridge or freezer and maybe a tv and pvr/dvd player and internet isn't that big a gen set. which means you don't need that much fuel.

It also means not breaking it out till you hit like hour 8 or so instead of it automatically failing over.

I have a duel fuel 2kw genset. so I figure I store 25 gal of fuel in my old car and 2 of the bbq grill tanks of propane.
Should be good for a few days before I need to get more fuel.

If I were going to power the whole house though, that would be a lot more fuel.