You didn't mention that you were only talking about
your tests on big pools.
And the pressure-on-unlucky-round-argument would only matter, if you switch pools right after such an unlucky long run (which wouldn't make much sense for you), if you just stay on the same pool it really doesn't matter, a lucky round will come and everything is fine again.
Anyway, i'm not saying one should use this, or that pool,
feel free to use whatever pool you like for whatever reason.
We all talking about our experience, there is no study/chart to corroborate PPS / size / stability.
Then, if I use PPS, its quite reasonable to assume that I will switch pools from time to time, and I am doing based on several factors, mostly based on pool load, if pool is under DDOS or experiences heavy load, it will serve me less getworks per second and my workers efficiency will drop.
If I switch on a small pool and it will suddenly see an increase of 30 - 50% in hash power, they may start experience payment difficulties if pool has a small wallet. I would like to avoid this.