Space is very harsh.
It then underwent extensive tests. Thus, to answer your question, yes, there are better processors for your desktop computer, but not for a space application of this nature. On a side issue, better processor is relative. You can have a 800 MHz Pentium III and still get the same performance as a 33 MHz 80486 if you don't have a bus structure that can handle the higher performing processor. There are a lot of trade-offs in designing a computer.