An update is available in(Xilinx Answer 34279); download the ZIP file titled "ar34279_v6_pcie_v1_4.zip" from the Answer Record.
The ZIP file contains a file titled pcie_clocking_v6.v[hd] which contains new settings for the MMCM VCO parameters. Place this file in your generated core's source directory.
Note that this ZIP file is cumulative and can contain fixes for other problems as described in (Xilinx Answer 34279).
03/04/2010 - Updated to refer to 34279
01/27/2010 - Initial Release