(How) can I reduce the loading time of GRASS-layers in UMN Mapserver?

[Wolfgang Qual]

Dear list,
I created a mapfile for two identical themes: One of them is a shapfile,
the other one is a grass vector dataset (connected via OGR). The 
shapefile contains a
*.qix-file which was created using the program shptree.
I compared the loading time for the two themes using the command "time
wget -O /dev/null "http://path/to/the.map". Result: the grass theme took
about 12 seconds (on a local machine), shapefile only 2s.
When I rename the dbln-file (file which sets connection to attribute 
table / database), the map is drawn as fast as a *.qix-shapefile. 
However, doing that will disable query-functionality. This would be 
important for me, though.

My Question therefore: is there a possibility to speed up grass layers 
in the mapserver application (something like shptree does?)?
Declaration of the grass-layer in the mapfile:

# OGR-Layer aus GRASS
#_# START LAYER l8
LAYER  NAME "l8"
TYPE polygon
STATUS ON
CONNECTIONTYPE OGR
CONNECTION
"/home/wqual/grassdata/muenchen/stadtbezirk/vector/block/head"
DATA "1"
METADATA
   LTITLE "l8"
END #metadata
### TYPE Polygon -- LEGTYPE 0x01 -- SYMTYPE 0x02
### singlepolyleg
CLASSITEM "cat"
CLASS NAME "Block_GRASS"
  COLOR 255 0 0
  OUTLINECOLOR 20 200 10
END #CLASS
#_# LAYER l8 QUERY
END # LAYER l8

I would be most grateful to receive some comments on this issue. Link to 
  the grasslist [1], where I asked the same question.

Best regards,

Wolfgang

[1] http://grass.itc.it/pipermail/grassuser/2006-March/032890.html
-- 
Wolfgang Qual
Landeshauptstadt München
Referat für Gesundheit und Umwelt
RGU-UW 11
Sg. 1 Gesundheits- und Umweltberichterstattung,
Energie und Klimaschutz
Bayerstr. 28a, 80335 München
Tel.: +49 (0)89 233-477 17
Fax.: +49 (0)89 233-477 05
E-Mail: wolfgang.qual at muenchen.de