There are a few more differences that weigh in favor of the HPX170
1 - waveform monitor built in
2 - slightly wider lens
3 - better low light performance
4 - more ND filter options
4 - SDI out for HPX - record the full HD Signal to external device if needed
Dan Brockett wrote a great article on Ken Stone's site detailing the differences
go here
HPX Features vs HVX200