RTL synthesis is relatively quick but produces a detailed output which is slow to process for a large chip - hence pre-synthesis energy and delay models are desirable.
Place and route will give accurate wiring lengths but is a highly time consuming investment in a given design point.
A simulation of a placed and routed design can give very accurate energy and critical path figures, but is likewise useless for 'what if' style design exploration.
A table of possible approaches:
| - | - Without Simulation - | - Using Simulation - | 
| Without Place and Route | Fast - Design exploration. Area and delay heuristics needed. | Can generate indicative activity ratios to be used instead of simulation in further runs. | 
| With Place and Route | Static timing analyser will give an accurate clock frequency. | Gold standard: only bettered by measuring a real chip. | 
| 52: (C) 2008-15, DJ Greaves, University of Cambridge, Computer Laboratory. |