There are 2 pretty active threads for the 500 EXC, but there has been no activity on the 350 EXC threads since early June. I'm thinking about one of these as both a lightweight dualsport and primary woods bike. I'd like to hear more about the 350.
Many years ago, I swithched from a 525 EXC to a 400 EXC and found the 400 to be much easier to ride on single track and more than adequate for dualsport / street duty. As much as I enjoyed the big power of the 525 in more open conditions, it was too much for long days of single track riding. With this expreience, I'm leaning more toward the 350.