Calavera PM'ed me yesterday with this question and I had to look up the max refresh rate in the manual because the video card in this system (a V5/5500 PCI) tops out at 75Hz at 16x12.
When I was shopping for my P225F, I did see a spec sheet on one site (I don't remember which) where the tube model listed for the 225F and 225FB was slightly different. If I remember right, the tube for the F ended in -3 and the tube for the FB ended in -4.
I've noticed that the 225F is becoming harder to find. I figured this, along with the slight difference in tube models, meant Viewsonic was phasing out the 225F. They have leapfrogged models this way before.
I've seen both monitors side by side and could not detect a difference in picture quality. And honestly, the difference between 85Hz and 99Hz is academic. You won't get a better picture quality by running at the higher refresh rate.
BHD