I have been imaging with a Stellarvue 80mm APO triplet piggybacked on a C11" EdgeHD on my AP1100 for the past 4 years in my observatory with no issues.  Both scopes produce nice long exposure images with PHD2 guiding on the AP1100.  I was toying with the idea of removing the 8 lb 80mm and placing it with the 22 lb 120mm.  This is still within the weight capacity of the 1100 and the accessories are minimal (autofocuser, FW, dew heater).  However, would you expect imaging results to suffer due to the additional weight or is this a matter of simply trying it, and see?