What about reducing total memory size available to Windows by changing boot.ini:

"MAXMEM=

Limits Windows to ignore (not use) physical memory beyond the amount indicated. The number is interpreted in megabytes. Example: /MAXMEM=32 would limit the system to using the first 32 MB of physical memory even if more were present."

Is SQL Server memory for file cache totally independent from Windows? If not, Windows may still use free memory outside of SQL Server for caching pages from SQL Server, which will affect the final modelling result.