Wells Fargo analyst Mike Mayo downgraded Zions Bancorp (ZION) to Market Perform from Outperform and lowered his price target for the shares to $50 from $62. The company's weaker than expected Q2 results help illustrate why larger and more diversified banks are preferable investments in the current environment, Mayo tells investors in a research note. Zions faces above average exposure to interest rate driven revenues without offsets commensurate with some of its larger peers, contends the analyst. He believes estimates for Zions need to come down and that the bank's and efficiency gains are likely to be offset by rate pressures. Mayo's top pick is Citi (C).