Regarding drive train losses, the value one obtains will vary depending on the dyno, but since dynojets are highly consistent from shop to shop, I like to go by them for estimating this stuff...
Based on multiple dynos from at least 9-10 different Z's, with SAE correction, this is what I've found:
Average power for 370Z or G37: 273 +/-5
Average power for Nismo version: 290 +/-5
Drive train losses for both AT and MT appear to be between 16.5% and 17.5%
You get a few outliers here and there; lower values appear to be associated with few miles on engine, suggesting incomplete break-in and compression may go up later on, resulting in higher power figures (unconfirmed).
Higher outliers could reflect everything from weather fluctuations to the ECU being unusually charitable with the max timing it allowed on a given run.
Also, you get some variance due to the gear dynoed in, with slightly higher readings associated with dynos taken in 5th vs. 4th.
Only other major factor is that lots of folks like to report STD corrections, which I find tend to skew optimistically for N/A cars.
Again those values are the average (arithmetic mean) based on a realtively small sample, with more data the numbers may be updated slightly (please send me drf's!!!!
).