Buybacks will exceed $600 billion this year for the first time since 2007 and make up nearly 30% of total cash spending, Goldman Sachs analysts estimate in a recent report, but that’s not what they think should be happening. While buybacks tend to give stock prices a quick boost, 43 months into a bull market with a looming Fed rate hike doesn’t seem like the right time to swap cash for shares. “Although buybacks do not represent an optimal use of cash at the current time, they will be positive for near-term stock performance,” write Goldman Sachs analysts David Kostin,…