I think with the 600, it boils down to the type of memory it has. When the 650 came out they updated the memory to be static, which should make it more stable, but I had other issues with it.

One big advantage to the windows mobile platform is you can move files where ever you want. This comes in handy with these sim games. If I want to try something risky, I just make a copy of the save file and move it to another dirctory. I was a little worried when I changed to it, but so far I'm very happy with it.