TMY3 Proximity Site

I am looking into the solar resource for a site located in Location A. The developer is anticipating about 80 MW of generation. The closest NSRDB sites are Location B, Location C, and Location D. I would like to get your opinion on which site would be the best to use as an approximate. I would also like your thoughts on using the TMY from Solar Prospector.
I would suggest running SAM with the NSRDB weather files from each of the sites, and also with Solar Prospector files for a few locations at and near the project site. By comparing monthly generation data (or whatever results metric you are interested in) from SAM for the different files, you can gain some insight into how sensitive your analysis is to the weather file. Also, I recommend the NREL Best Practices Handbook for the Collection and Use of Solar Radiation Data ( PDF 7.5 MB ) to learn more about the different sources of weather data and impact on modeling. It is written for concentrating solar power (CSP) audience, but is also useful for photovoltaic modelers.
UPDATE FEBRUARY 2015 Here is a reference and link to the updated Best Practices handbook: Sengupta, M.; Habte, A.; Kurtz, S.; Dobos, A.; Wilbert, S.; Lorenz, E.; Stoffel, T.; Renne, D.; Myers, D.; Wilcox, S.; Blanc, P.; Perez, R. (2015). "Best Practices Handbook for the Collection and Use of Solar Resource Data for Solar Energy Applications." NREL Report No. TP-5D00-63112. ( PDF 8.9 MB )
Best regards,

Paul.