RE: which mechanicals?
I agree with both the Steelhead and Snyper recommendations. Even if your bow is tuned perfectly I would still recommend both heads as they provide much less of a chance of wind planing....both in terms of actual bow speed and because of actual wind conditions.
If both of these heads work well for you then maybe you might want to try something with a little larger cutting diameter. Then you can really take advantage of some of the expandables out there.