Replacing HD in a Blueberry iMac

I have a blueberry iMac 350Mhz with USB only. It currently has a 6 or 7GB HD
in it that is dying a very slow death. I am assuming it is an ATA33 or 66
IDE 5400 RPM, pretty sure it's a quantum.

If I were to replace that hard drive as it is dying, with a ATA 100 running
at 7200rpm would there be any ramifications to any componentry inside the
machine?

ie. There is no fan, would a 7200 rpm drive create greater heat? If it is a
ATA 33 or 66 bus is there are problem installing an ATA 100 or is it just
not possible. Here are my choices, please comment on the most
appropriate/possible.

ATA 66 5400Rpm
ATA 66 7200rpm
ATA 100 7200rpm

Obviously the latter two are the most readily available.

Thanks