Salary information resources for IxD's

I'm looking for good salary data for IxD's.

I've seen the following:

UPA's Salary Survey:
http://www.usabilityprofessionals.org/upa_publications/upa_voice/volumes
/2006/june/2005_upa_salary_survey.html
AIGA's: (http://www.aiga.org/content.cfm/salary-survey)
A study at Spirit Softworks:
http://www.spiritsoftworks.com/resources/2004-salary-survey.htm

The numbers seem to vary quite a bit and the focus is really
not on IxD's.

Thanks,
Russ