It's not power, it's torque that kills the clutch.
Stage 1 K03 has less power than a standard Audi S3 with same clutch, but the mapped GTI will have enough torque to kill the clutch.
As MC says above, there isn't really a set limit. Some clutches will slip at stage 1, other won't slip untill stage 2+.
Typically as these cars are getting older and higher mileage, it's more common for clutch slip at stage 1 on normal GTI & Ed30.
My advice would be to budget for a clutch alongside the cost of a remap. If it doesn't slip straight away, it will eventually