So it's cranking, just not starting? If that's the case, it wouldn't be starter motor. To eliminate that, try jump starting it. If it starts, that'll be the problem. It still would explain the problems under boost.
I would have said coil packs, but you've said their spitfires so that wouldn't be it. Have you had any work done to the car recently?
Check the ignotion system. Is the car getting spark? Is it getting fuel? Are there any plugs that have fallen off? All the vacuum lines attached? I'd check all these first, and then take it to a mechanic.