Right now I have FTTC and haven't switched to 5G because it's not as stable. I don't mind the speed fluctuations, but latency spikes are annoying. FTTC, while 3x slower, is more consistent. On the other hand, my experience with ADSL was bad and if I had 4G back then, I'd take it.
By the way, not every network is equal when it comes to stability. Here in London I see more latency spikes on Three than I do on EE, for example. Vodafone used to be between the two.
Something to keep in mind in your case cancunia, is that B20 is useful for base coverage and better indoor signal, not performance. If you get your signal from a B20-only far away site that gets busy from time to time, the experience won't be as good as the alternative near you with B3.