That may be the truth with our 1st generation 4.928's, but we discontinued those years ago and replaced them with our revised 4.923's which are currently the strongest (and lightest) 4.9 final drive on the market. I would NOT recommend the 5.1 for a rally car though.
At the end of the day, it doesn't matter what brand you go for; they will ALL break on a rally car, regardless of what "brand" people tell you to purchase. The only way to not break a final drive is to lift off the throttle when going "superman", which 90% of drivers are unable to do.
Put simply, purchase whatever is going to cost you cheaper to replace, because final drives will not be covered under warranty when broken in a rally car. Or you can learn to lift off the throttle at the right time.
Also, bit of advice: The shorter the ratio, the more likely it is going to break due to the smaller size teeth on the pinion gear. This why hardly anyone every breaks a 4.7 FD (including oem), whereas nearly everyone breaks a 4.9 (regardless of brand).