Not sure what delay models they use , but ...
Pre-route timing does not use extracted RCs based on the pdk tech files. What it will do (i think) is a simple steiner route (ignoring shorts) and then use the capTables to look up estimated RC values on the nets.
This is normally fairly accurate (within 5% or so). If not you can create a extracted spef and then correlate it with your estimated spef. You can then using scaling factors to get your estimated RCs to match the extracted ones.