I'm running long term experiment on breeding Ghazt with 10 permanently lighted torches. Results so far:
Total breed count: 149
| Monster | Count | Probability, % |
|---|---|---|
| T-Rox | 130 | 87,248 |
| Ghazt | 19 | 12,752 |
Breeding bonanzas and rare reprises are carefully avoided. So the conclusion is: you need ~10 breedings with 10 torches lit to breed Ghazt. With bonus breeder it's easy task.