Yeah i do the same with the IP each nginx process knows the machine to locate via http://172.0.0.1; each machine is assigned its own localhost ip.

The only thing that does not use the IP is each servers nginx pulls from static data from the mapped hard drive Z:/ But taken into consideration i run SSD's and i also use a RAID6 setup with the following LSI Mega RAID.
http://www.lsi.com/products/raid-controllers/pages/megaraid-sas-9271-8i.aspx

And a CacheCade 120Go SSD to cache frequently accessed data.

I also think Nginx open_file_cache feature would help allot too. I dont get any timeouts or lag or problems with static data requests.