Hi all,
I was struggling to get some of the larger scenarios to run smoothly with the meager spec i have which is:- win7 64, 3gig ram, dual core 2.5 celeron, 1 gig nvidia graphics card. after tweaking a little with the graphics card settings & game menu settings set to fastest rather than quality i found i could still only scrape through the bigger battles with 'trees off' and anything else which made it easier on the system.
Then i found this little program down at cnet.com
http://download.cnet.com/RAMBooster/3000-2086_4-10028673.html
Its free and there is a little tutorial on youtube to follow which i found useful, after installing and trying it out i found it greatly improved the game performance, especially on larger scenarios. If anyone else is suffering from sluggish gameplay on larger battles give it a try and see if it helps.
cheers