UPDATE:
I have appeared to have solved my issue with dropping frames. When I updated MSFS to SU11 (40th Anniversary Edition) I remember to empty my community folder before installing. However, I did forget that sometimes there is an issue if you do not delete the rolling cache within MSFS.
After going to Options > General Options > Data and selecting Delete Rolling Cache from the Rolling Cache Settings section, restart the simulator and now the A310 runs very smooth at 43fps or higher at 4K in Ultra settings on my system.
Your milage may vary, but worth a try.