427Roush

The stock powdered-metal connecting rods are generally the three-valve motor's weakest link. People have seen random failures of stock rods as low as 450 hp; "500hp and higher for an extended time period will definitely break them."
Pistons disintegrate (detonation): Although not that strong, the stock pistons outlast the rods. But with detonation, the pistons can shatter into pieces. Replace the stockers with quality aftermarket forged pistons. This is from an article in Hot Rod Magazine.

Mr. D

The Roush shop that did my car has built many 575 HP Supercharged 5.0L Mustangs without one coming apart! I think if you drive them with any sense you won't have problems!

I'm getting 475 HP out of a 4.6L with my set of parts and tune and it runs like grandma's grocery car until you put your foot in it! I have very high differential gears and it pulls much like a older Shelby, but with less grunty torque. 0 to 60 usually around 4.6 Sec. It get's 27.5 MPG at 80 too!