Does anyone know here by chance 

a) where to get full 68040 processors for cheap
b) whether or not a 33 Mhz processor would also work in a 25 Mhz machine
(like C 610 or Q 605 or LC 475)? 
c) if a 25 Mhz processor in 33 Mhz machine would break because
overclocked?

Thanks in advance for any advise and suggestion,

Ulrich