IBM's ( IBM) rumored attempt to buy Sun Microsystems ( JAVA) may be music to the ears of Sun's investors, but the jury is still out on whether a deal would be good news for IBM shareholders. Whereas Sun's stock exploded on the M&A talk, rising more than 77%, IBM's shares fell 2.32%, despite a broad rally in tech stocks that saw the Nasdaq rise 0.64%. Although an acquisition would undoubtedly create an enterprise IT behemoth, IBM needs to carefully consider the impact of buying Sun, according to Goldman Sachs analyst David Bailey. "We would question the short-term and longer-term benefit to IBM from a potential combination," he wrote in a note released Wednesday. "While there would undoubtedly be significant cost savings in the hardware divisions of both companies post a potential acquisition, there is also substantial overlap in almost all product lines." Perhaps the biggest challenge for IBM, however, is taking care of the execution problems that have hampered Sun in recent years. The Santa Clara, Calif.-based firm, for example, struggled to swallow its acquisition of StorageTek in 2005 and is seen as one of the tech sector's big underachievers. Despite repeated attempts by Sun's management to put its house in order, the company's stock has been in retreat for months, and the firm's revenue tumbled 11% year over year in its recent second-quarter results. Sun's business model is less resilient than that of IBM, which has largely avoided the worst of the global economic crisis, partly thanks to its software and services businesses. Whereas IBM can depend on these recession-resistant divisions for revenue, Sun typically relies on a more traditional business model, according to Bailey.