The Landscape Institute has published guidance on photography and photomontage:
Photography / photomontage question 1/13 (Jun 2013)
Sensor size and crop factor
Photography / photomontage question 2/13 (Nov 2013)
LI Advice Note 1/11 (March 2011) Advice on photography and photomontage
This guidance is in the process of being revised. Please note that it is likely that the LI will be encouraging the use of full-frame sensor cameras in more demanding situations.