Speed difference between 3.6.1 and 4.6.0

[Steve Young]

Hi folks,

I have two mapserver sites running. One on Mapserver 3.6.1 and the other
on 4.6.0

The 3.6 site is on a Duron 750 with 256Mb RAM and an IDE drive.
Webserver is Apache 1.3x
The 4.6 site is on a Celeron 1.7GHz with 256Mb RAM and a similar IDE
drive. Webserver is Apache 2 

Both sites use an identical interface and have the same datasets. The
4.6 has a few extra raster tiles in full colour.

My issue is the 3.6 site is at least twice as fast at creating a map
image as the 4.6 site. This is when they  both have the same datasets
and extents selected and the same (gif) output format. Speed difference
appears to be the same for either raster or vector. I've used
tileindexes, shptrees and sortshp to optimize speed on both sites so I'm
starting to look beyond data any differences in how the data is
presented to the the sites. Has anyone else had a similar experience or
has any ideas? Currently I suspect it might be down to build
differences. Is that feasible?

Thanks for any help.

Steve

MapServer version 3.6.1 OUTPUT=GIF OUTPUT=PNG OUTPUT=JPEG OUTPUT=WBMP
SUPPORTS=PROJ SUPPORTS=TTF SUPPORTS=WMS_SERVER INPUT=TIFF INPUT=EPPL7
INPUT=JPEG INPUT=POSTGIS INPUT=OGR INPUT=GDAL INPUT=SHAPEFILE
 
MapServer version 4.6.0 OUTPUT=GIF OUTPUT=PNG OUTPUT=JPEG OUTPUT=WBMP
OUTPUT=PDF OUTPUT=SWF OUTPUT=SVG SUPPORTS=PROJ SUPPORTS=FREETYPE
SUPPORTS=WMS_SERVER SUPPORTS=WMS_CLIENT SUPPORTS=WFS_SERVER
SUPPORTS=WFS_CLIENT SUPPORTS=THREADS INPUT=EPPL7 INPUT=POSTGIS INPUT=OGR
INPUT=GDAL INPUT=SHAPEFILE