Some of my research on anxiety and performance is now available in France: angoisse (worry), anxiete, optimisme, pessimisme, et cognition.
Across five data collection points, optimism was found to be inversely related to anxiety, but did not predict a stronger performance on difficult tasks. Out of all of the variables studied, worrying actually resulted in the strongest performance for complex challenges such as successfully completing law school.
The Takeaway: Being a worrywart can actually be helpful in the short term to put a fire under your butt, while optimism does not have a significant correlation with actual success￼. Worry can sometimes make us get difficult things done.