Could you please confirm the lower limit of 220kV three phase line loading?
For steady state stability delta should be between 30 and 45 degrees, and
so steady power transfer can be P = 220*220*sin37.5/(400) ie nearly 60.5 MW
to 85 MW. (SIL=120).
The suggested loadbility of the line of 60.5 to 85 MW (0.5xSIL to 0.70SIL) is for a large line of 600 mi(965 km) corresponding to the stability region as shown in the curve below.
For shorter lines, the line loadbility may be within the thermal region and could be as high as 360 MW (3xSIL).
