My GE oven has a convection selection as well as a convection ROAST selection. Not sure when to use one or the other as well as what the conventional wisdom is on the subject. I'm sure you have delt with this Q before.
Check the manual. If you don't have it handy, iyou should be able to find it online. That said, I was told by the cooking expert who does demos at our local Dacor showroom that convection roast -- at least for my Dacor range -- should only be used for very large roasts. In my range, it provides more heat in the bottom half of the oven. I always use pure convection for roasts -- it works perfectly. But then, I typically butterfly my chickens and turkeys, and most other large cuts of meat I braise-roast, where the cooking happens inside a covered pot. ;o)
I have the GE Monogram wall ovens, and I like to use the convection roast setting for roasting a whole chicken. It produces a beautifully browned crispy skinned bird on the outside while the inside (white and dark meat) remains both moist and juicy. Roasting at a high temp on this convection setting is somewhat similar to rotisserie cooking due to the fan that produces an even heat. Check out this blog entry of mine for a simple roast chicken...
I use the convection bake setting mostly for cookies because it ensures that the tops are done without the bottoms burning. When baking with the convection setting you need to be attentive to the time as things tend to bake faster. Hope this helps.
Yes, if your oven does not turn the temp down automatically, turn the temp 25 degrees lower