php-fpm / nginx random php lock ups php 5.3.10 w/ nginx 1.0.12

[Stefanita Rares Dumitrescu]

hi guys, i have a problem.

i have a high end server - dual quad core xeons, 16 gb ram, 4 x 120 gb 
ssd's in raid 10, and a gigabit pipe. i only host 1 site on it, and from 
time to time the php simply locks up, restarts, and during that time, 
the users experience 5-10 seconds load times on pages.

i have around 1000 1500 concurrent users at peak times on the website.

here's what happens in the php-fpm.log:

http://pastebin.ca/2131186

some of those scripts that you see as executing slow, are like 4 - 5 
lines of code, so it's pretty impossible to be a coding issue.

here is my php-fpm.conf:

http://pastebin.ca/2131189

if you guys couuld help me shed some light on this i would much appreciate.