The only thing the Mac RAM vendors do is test RAM to make sure the batch they have is fine (for now).
There are RAM batches that will have a few bits that does fall behind and will give you problems. The PowerPC architecture is not tolerant to bit falure and so you have to find RAM that does not fall behind the CAS3. I think most so called "Mac RAM" vendors are VERY overpriced for what they offer, but do get quality RAM and a brand name/vendor that has a warrenty arround their product.
Save your money (and troubles) and get CAS3 and PC3200. But different speed (specially if its slower) should not work. Different CAS should not be a problem as the machine will drive them all at CAS3. Well - not a good thing that is for sure.