Sorry, my fault - the GTLs on the UD3P are just one setting called 'CPU reference', this changes with your termination voltage (VTT). By default, your CPU ref is 0.76 when VTT is also at default of 1.2v. For me, increasing CPU ref to 0.785 then increasing the VTT often gave best results, but occasionally needed to go up or down one on the CPU ref to get stable. This is different for everyone's configuration, but should still be around that region (i.e. one or two up or down from default). As for skews, increasing them as you increase FSB can yield better results at higher than ~475 FSB, seems even more crucial for benching at 530+ FSB. I found CPU being 50ps less than NB skew often gave better stability , but sometimes equal values worked better.