OK, I got some definitive info from Dixondale. Most short-day onions are sweet (I hate that term, because we're not talking "sugar" sweet), and what makes them sweet is higher water content. Higher water content leads to shorter storage lifetime. So almost no short-day onions are storage onions. However, Red Creole is a short-day storage onion that is not too sweet. Kinda pungent. I'll probably put some of those in later this year to extend my onion supply beyond my sweet onions.