I am confused why you are running a 53/39 with a x-23 (is that 11 or 12?) if you know the biggest gear you can run is 53-15.
Better options: Shimano -
http://aebike.com/page.cfm?PageID=30...ils&sku=FW6606
Campy -
http://aebike.com/page.cfm?PageID=30...ils&sku=FW9032 or
http://www.probikekit.com/display.php?code=L4039
These options will have you blocking off less of your cassette and allow you to have both more useable gears and a larger gear or two for climbing. You could also build your own mixing cos from other cassettes.
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