MORE RAM
i have a very big route as well with about 170 baseboards and 60 to 70 locos al running at the same time each with rolling stock,i am using vista altimate with 4gig of coirsar ddr2 ram with 2X nvidia 8800 gtx videocards with 760 odd of ram on each card, and mine runs very smooth,however the more ram the better ,but it also depends on your motherboard ,cpu ,videocards or card,ram,each of these bits of hardware are conexted to the other so if one isnt at the top of its game ,,or the best quality,it can and it will lag the rest of the hardware which will show in the game ,before you buy new hardware check and do a review of it .all you have to do is type the hardware name and model number into a search engine and type review after the name and model number.good luck
steve123