I've replied in the other thread, and I think we've reached the same conclusions.
What I mean by 'moving the world' is this. Not sure this explanation is going to be very good, by the way...
Rather than painting by waggling the mouse backwards and forwards you hold the mouse still and use the arrow keys to 'move the world' underneath it. For example, line the track up so it's left to right across the screen, begin painting (I use a 25 brush down the centre of a double track) and then press left or right. As long as the brush weight is sufficient you'll get a nice straight line. Of course you can also move the mouse about in conjunction with the arrow keys to follow curves etc.
Using this method I've also found that it's relatively straightforward to get the different textures to blend neatly. From my trackbed example earlier you can actually see the two textures being 'sucked' towards each other as you go. I've also concluded that it's quicker to do this using larger brushes and touching up any odd bits afterwards with a smaller brush than it is trying to do the same with a small brush in the first place.
Personally I hate the plain green grass, and I never leave any area unpainted in my routes. Maybe this is a bad idea, but I just can't help it!
Hope that makes sense!
Cheers
Bob