Key TakeawaysOppenheimer analysts stuck with their "outperform" rating on Costco Wholesale on Thursday after the retailer posted strong December sales numbers.Catalysts for Costco's shares "include a potential stock split," the analysts wrote.Costco shares closed Wednesday at $927.37 and are up 41% in the past year. Oppenheimer analysts stuck with their "outperform" rating on Costco Wholesale (COST) Thursday after the retailer posted strong December sales numbers, noting that catalysts for its shares "inclu ...