You have to remember that you have a chipset limitation of only ~3.3gb of ram usage with the E1705.
Using 32bit or 64bit of Vista will not change this.
Also, like zzpulp said, Vista's index score is no big deal.
It is a very rounded and subjective score that has no real meaning when it comes to performance.
You are better off keeping the 4gb of ram in the system as it will allow many memory hungry/intensive programs to run better.
All you are doing is getting all worked...