Yeah, it's possible. You will (probably) have to create your own custom resolution settings to experiment with high Hz. There is a screen for doing this in the NVIDIA and AMD graphics driver tools.

For your custom resolutions, you might have to use low width×height dimensions when using something high like 120 Hz, but this depends on the monitor you are using. The custom resolution screen in the graphics driver tool will show you the "kHz" (kilo-Hertz) for the clock signal for your custom resolution. There is a limit for that kHz signal and this depends on your CRT monitor. If you go above the limit, the monitor will shut down and refuse to work. You can see the kHz limit printed somewhere on a label on the back of the monitor.

 

My old CRT monitor (which is currently stashed away in the attic because nostalgia won't let me get rid of it) has, that I know of, the highest horizontal frequency of consumer displays before they stopped making them, which is 140 KHz. That equates to a resolution (which I felt was a good compromise) of 1600x1200 at 110 Hz. Like deepor said, you can create a custom resolution in NVCP, and I used to run mine at 1600x1200 at 100 Hz.

Now, if you're still interested, in order to get 120 Hz out of a CRT, you're going to have to buy one of the best ones still available and run a pretty limited resolution. With a FW900, you could probably get away with more because of the aspect ratio, but you're limited by the vertical resolution anyway. If you get one like mine, 1600x1200@100Hz is guaranteed, but not a single pixel higher, I figure.

 

I could have sworn there was a Philips CRT that could do 185hz at 1600x1200 but all I can find is the Philips 202P40 and that's limited to 85hz @ native 2048x1536 and ~120hz at 1600x1200.

https://www.cnet.com/products/philips-brilliance-202p40-crt-monitor-22-series/specs/