...actual valve lift at the retainers with the race valve springs will never be as much as the advertised valve lift...
That's entirely dependent upon how the rocker arm is designed. AndyF's rocker arm articles touched on how some of the brands he checked were "over-ratioed" w/ checking springs, but came in at or above the advertised ratio when checked w/ the actual valve springs.
As far as deflection, I believe it can be in the pushrods, the rocker bodies, and/or the shafts, depending upon the components used. Not sure Joe Average's budget can eliminate it entirely, but I've seen some cases where it certainly went beyond my idea of an "acceptable" amount in terms of lift/ratio loss.
