If you have 4" of overhang then I'd definatly try to install some venting in those soffits. Since these are the air intakes they're needed in keeping your attic cold and providing airflow. There are a few different types of vents you could install like what's on the following links. This first link would be the easiest
http://www.duraflo.com/siding/soffitseries.htm
These next two would require modifications to the roof edge
http://www.airvent.com/homeowner/pro...ventedDE.shtml
http://www.dciproducts.com/html/smartvent.htm
And you'll surely want to remove the insulation from those soffit cavities and install the ventillation baffels to keep the channel open. This link here' will help you out some in that. Best to staple them on the sides of the rafters using galvanized stapels.
http://www.rd.com/content/openConten...ontentId=18231
You'll need to also block all the warm air entries into the attic. Like using the spray foam to seal around the plumbing stack, electrical raceways, etc. Also insulating and weatherstripping the attic hatchway. Along with making sure any bathroom exhaust fans are ducted out the top of the roof. And if there's not a vapor barrier under your insulation then consider painting your ceiling with a vapor retarder paint.