I've read some people/sources say "the timing must match or it won't work". This is not true at least for the Supermicro boards I've tested this on.
Some examples:
PC2-5300F-555-12
PC2-5300F-555-11
etc.. Notice the "12" and "11"
Also the ones that have a "PC2-5300F-555-11-B0" or "PC2-5300-555-11-D0" are also fine.
What happens is what one would expect, the........