I think you should refer to "design of portal frame buildings" published by the ASI, woolcock is in favor of either using the current deflection limits and 20m/s or adjusting the deflection limits to use 25m/s. either which way I think you will get the same answer.
"Programming today is a race between software engineers striving to build bigger and better idiot-proof programs, and the Universe trying to produce bigger and better idiots. So far, the Universe is winning."