Some say that to install Trainz, outside of C

rogramFiles, is proper, as this avoids the UAC warning notices.
I would install everything you have ... as your PC has more than enough room for all US, AU and UK assets (you will never even know that they are there ... cluttering up your Trainz file ("Local" I believe) ?
Some of those foriegn country files are "Built In" assets, and deleting them will break some "Built In" routes.
I have a 2Gb Integrated Graphics Toshiba Satellite 105 that, plays TRS2006 very well (some choppyness of framerates).
Higher versions of Trainz will not play on my 2Gb Integrated Graphics laptop, as Trainz really likes a dedicated video card.
If you are bothered by all the foriegn country assets, I would delete them one at a time, checking that they are not "Built In" assets (it will take years) ... lol !
With my 2Gb Integrated Graphics laptop and, I downloaded every asset known to mankind, and my "Local" file in TRS2006 had hundereds of thousands of US assets ... and my disc was almost full ... causing my cheepo laptop to lag ... not to mention my Trainz "Railyard" scroll down list was never ending.
A 6Gb laptop is huge (enough to hold the contents of the Library of Congress).
I think Trainz will only use 2Gb-3Gb and possibly 4Gb maxed.