I actually have first hand experience with how shitty they are.
They are fine for street cars that do drag.
The block can only take about 400hp safely before you risk cracking it. For an iron block V8, this is really weak.
As for the circuit, the oiling system is really weak. A good friend of mine took his 5.0 to Dunnville and blew it up on the third lap. At the time, we thought this was because his rev limiter was set to high. He got the motor professionally rebuilt and lowered the limiter to the factory 5500rpm. The next track day he went to, the same thing happened.
Its not only his car. The last time I went to Cayuga road course, there was one foxbody running with a 5.0. Guess what, that car blew its motor too due to oil starvation.
This is why I think the 5.0 is shit.
If you plan on taking your RX7 with the 5.0 to the track (road course), I hope you invest in a really good wet sump setup like accusump or just go dry sump.