Question about the old imac max. RAM speed

[oddfuzz]

i'm looking to upgrade my Graphite imac (600 MHz) with more RAM, again. I was looking into getting a new mac very soon, but then the pentium switch was announced, and even though mine's kind of a dinosaur, it's been an incredible machine and i figured it could last me a nother year or so. with that being the case, i decided i should get some more RAM to tide me over and help out the old geezer. SO, here's the deal: the stardard was 128 pc100 and i got 256 pretty soon after that from some online store. system profiler shows the 256 as pc133 so i assume that it's running it at 133, but after looking for a little while for more memory today i came accross some 133 that said this new kind is no longer backwards compatible with pc100. I was wondering if this could mean my mac is not running the 133 up to speed, after all, the system bus is only 100. Are bus speed and RAM spead connected at all? i really know nothing about RAM and all the specs i could find listed the minimum RAM speed not max. Thanks for any help. I'd love to save 50 bucks if i really don't need the 133.