RE: Enough KE for Spitfires?
35 yards is pushing it.
I am guessing your speed is about 235 to 240 fps. You arrow probably weighs about 440 grains. The speed and weigh are both just estimations. Making these assumptions....your KE at the bow is 54 ft-lbs. At 35 yards your KE is 46 ft-lbs. I think this is marginal at best. In my personal opinion (remember opinions are like butt holes....we all got' em) 20 yards is the maximum distance I would shoot a mechanical from your bow.
You could probably get a mechanical truth the ribs with no problem but at 35 yards it would much easier to hit the shoulder. I don' t think a mechanical would make it through the shoulder.
Hope this helps you make a decision.