It would be nice if Boeing would provide a suggestion in the FCTM of the recommended course of action in the event of Airspeed Unreliable during or after takeoff, but they don’t.
This leaves thinking pilots trying to work it out for themselves, hence this thread (and it isn’t the first, this has been discussed on this forum previously).
I’ve noticed that it creates two schools of thought: those who would maintain TOGA thrust and TOGA attitude until a safe altitude, and those who would commence the memory items at 400 feet.
To my thinking, both options are “safe”. As to what option your airline or your simulator instructor is looking for is probably best discussed before you do it.
My airline exposed me to it in a simulator a couple of years ago at 32C, 79.0T (ie MTOW) Flaps 5 at sea level. He made us observe the rate of climb once we got to 10/80% - it was in excess of 1000fpm. Way in excess of an engine out scenario. That was good to experience, because now I know. I didn’t know prior to that and may have had trouble believing it.
Reducing thrust to 80% and lowering the nose 5 degrees after taking off at MTOW in a hot climate is not something that would be considered naturally safe unless you had seen it before.
One objection to delaying the memory items is that it delays turning F/Ds off. We are accustomed to follow the F/D pitch bar on takeoff, and with Airspeed Unreliable, the F/D might take us somewhere we shouldn’t be.