Just looking at the clips in fcp with the scopes up and my broadcast monitor on I can't tell any difference just a note
Heres what it says about gamma correction directly from apple
Apple ProRes Tips
This section lists some practical tips for working with Apple ProRes codecs.
Apple ProRes codecs have a native gamma of 2.2. The Gamma Correction setting in the advanced compression settings pane allows you to disable the automatic 1.8 to 2.2 gamma adjustment that can occur if RGB material at 2.2 gamma is misinterpreted as 1.8. In some cases this gamma adjustment is not desirable (for example, if the source image is RGB 2.2, or if the encoded Apple ProRes file is meant to be used in another RGB-based application).
Automatic: Select the Automatic setting to have the Apple ProRes codec convert RGB 1.8 gamma source media files to 2.2 gamma.
None: Select the None setting to disable the adjustment of 1.8 gamma to 2.2 gamma.
So is the better question to ask is the pdw-700 camera recording at 1080p23.98 50mb @ XDCAM HD 422 , is it already a 2.2 gamma or does it record in a 1.8 gamma?
That being said, a professional video camera will record files in a YUV color space (as opposed to images created in a RGB color space) and will not need gamma correction when converting to Apple Pro Res. so, for conversion of your XDCam files, you can select None.