So when you rev the car out it stops at 5,000 rpm? If so, methinks thar be an
ecu/tune in there.
What other mods are on the car and have you performed any mods/tuning since purchasing?
Before towing the car places, call up the workshop and ask what they will do. Since you are essentially wasting the time of the workshop asking them to put something in writing when they will be getting no work out of the job, they might not be too interested in that. Most workshops will be able to tell you its 99% a big end gone, but putting that in writing without stripping down would be hard. Once the engine is stripped, getting the dealership to look at warranty would be hard too, I would think.
I would recommend a mobile Subaru mechanic like Jim from Blue Star to avoid a towing fee again.