Problem with large static files

[etrader]

I have a strange problem with slow load of relatively large files. On a
domain without proxy (designed for serving static files), the request
time (as monitored by access log $request_time) for an simple jpg image
file of 5KB  is 0.000s (seems to be shorter than 1ms). Thus, one expect
to load an image file of 15KB within 3ms, but surprisingly it takes
about 600ms. A static file of 15KB is not big at all; but there should
be a threshold which leads to this slow down upon slightly increasing
the file size.

Posted at Nginx Forum: http://forum.nginx.org/read.php?2,220272,220272#msg-220272