Manhattan makes a really good point, When insulating an attic in our area the best thing to do is to condition the space. This goes for any time you have mechanicals in the attic also. An air handler with all that duct-work works much less if the area around it is acclimated to the season.
The insulation job has to be done correctly however, I have even seen the pro's put it in backwards. Consider who is installing the insulation and what part of the country do they come from.
Insulating the rafters is a good way to do this ,proper soffit and ridge vents with prop a vent work fine. The issue shows up when your rafters are 2x8 and you cannot fit r-49 in that space.
We would go to a foam insulation at that point with no venting, a whole different animal.
Hope this adds some thought.....
I'm scarce around these parts lately due to a brisk business.
I miss you guy's....