(This story is for CNBC PRO subscribers only.) Here are the biggest calls on Wall Street on Friday Jefferies upgraded Six Flags to buy from hold Jefferies said in its upgrade of Six Flags that it sees 50% upside and has "confidence" in an attendance recovery once the coronavirus fades. "Although the environment remains challenged, the earnings power targets have been set at achievable levels, which implies 50% upside that should price into the shares as the execution begins to come forth. Our upgrade to Buy is a reposition to capture this forthcoming performance." JPMorgan upgraded Spirit to overweight from neutral JPMorgan upgraded the discount airline and said it was well-postioned to return to profitability as compared to its peers in the industry. " Spirit 's fourth quarter guide was refreshingly differentiated from peers, insofar as it results in a slight improvement to our earnings forecast but more significant improvement in our liquidity forecast. ....