Here is some interesting testing looking at the relationship between screen modes and resolution compared to FPS using FRAPS. Trainz performance settings were not altered during these tests. I have a good sound card and was taking its output via fibreoptic link into my entertainment system with stereo sound 2.1.
My normal work setup is dual 6800GT graphics cards with 256MB on board with a 2GB memory. I use dualview with nVidia 93.81 operating two 17inch Philips LCD monitors. This is especially useful for working on Trainz repairs as I can have multiple applications open on one monitor while observing Trainz or CMPSP1 on the other.
I tested Agathas Country 1

1022 version) with tour 2a session. I ran several trains but this comparison is based on Driver Adair and Silver Jubilee loco hauling a string of coaches.
In dualview with nothing open on second screen and at 1024x768 res I got 0-5FPS hence the severe stuttering. It matters not whether CPU is running at 30% or 100% stutter much the same.
Using a single monitor i could increase this to 6-10FPS. Still quite a lot of stutter.
Surprisingly I could clone my 29inch TV which also has 1024x768 res without any deterioration in the FPS. Pix on TV absolutely stunning Keith.
I then went to SLI which parallels the two video cards and upped the res to 1280x1024. Stunning pix but ~6-12FPS.
I then went into Surveyor and raced around the scenery achieving about 32FPS max.
I dropped res to 1024x768 and FPS shot up to 60FPS max. (I'm operating on 60HZ with no overclocking so probably wouldnt get any more than that.
Back to Driver and we are now at 10-15FPS at the lower res which is also the native res of the LCD monitors.
Now without altering anything I then loaded British Rail 2004 and achieved between 20-60FPS while the train was running in SLI mode, external view camera and 1024x768 res.
Quality of sound is dependent on stutter rate. Note the train speed surging appears related to track and junctions not stutter.
My conclusions from this are that the image weight of Agathas Country 1 version :1022 is heavier than my system can handle. I may get some improvement by increasing my memory to 4GB, or by reducing applications and utilities according to Program Manager running in the background.
There's about 80 of these but I have yet to determine what I could safely disable during Trainz operations.
British Rail 2004 is 40+MB and has only 415 dependencies, mostly builtins, compared to Agathas Country 2,120 dependencies. The difference in FPS rate and thus stutter is quite wide.
How about someone else from UK doing a similar comparison so we can see the relative performance on a different machine.