Re: Forcing 60hz with twinview.
This seems to be a problem:
(II) NVIDIA(1): Not using mode "1280x1024" (vrefresh out of range)
If you remove this option from your X configuration, does that have any impact?
Option "VertRefresh" "DFP-1: 75"
Or if you uncomment and use the "1280x1024_v" mode in your X configuration, does that have any impact?
Or if you broaden the VertRefresh range that you specified for 'Monitor1' does that have any impact?
Also, please generate and post a full bug report.