SUP ESR!

Let me tell you my predicament.

I am currently running dual CRTs. however my main has lost its blue gun, which has 120hz. My secondary is fine, but only uses 100 hz. I have another available however it is also 100hz.

SO to put a long story short:
Is there a noticeable difference between 100hz and 120hz? Is there no substitute for 120hz, even if the monitor is yellow??

Thanks in advance :).