while RC does support WLMs, the recommended flow has been the use PLE (Physical Layout Estimators) for several years now. PLEs rely on DEF, LEF, and capTbl information hence provide the most accurate modelling. As per exercise in correlation, you need to take to preCTS to really do meaningful correlation. A TLU+ vs PLE number will be comparing apples and oranges. You can go into RC and/or DC and generate a SPEF to be read in the other tool but a flow of reading SPEF and optimizing is quite useless since the only to keep SPEF annotation meaningful is to not optimize.
hope this helps,