It's very expensive for Herculus , assura . If you are doing extract rc only , you should choose star-rcxt .
The others have more functions than extract rc ( drc , lvs , lpe ) .
assura is not officially supported by Foundry, cadence maintain the runset. Hercules should be good choice, in my case, variation is around 5% between post-layout sta result and real chip. Any input for xCalibre?