I'm wondering if the max fanout default = 5 setting is considered at all. For example, the default regression output of the zipdiv design shows fanouts > 10 (for all synthesis results):
Report: _2003_: 65
Report: _1968_: 68
Report: _0081_: 32
Report: pre_sign: 68
Report: r_busy: 65
Eventually the reason for the slow design performance. I see similar problems on other designs.