I'd have thought that if you'd watched since '78 you'd have worked out that both averaging 48 striking at 75 and 40 striking at 70 are unrealistic as a
minimum standard. S/R 50 with the ball also isn't - for example it excludes Anderson and Broad (and average is more important anyway).
@sayon basak is right, it depends on the team. It also depends on the vagaries of the team's selectors, some like to chop and change more than others. Averaging mid-30s with the bat or 31 with the ball would get you a good run in many middling teams, but it won't keep you in a very strong one, unless for a specific role like a spin bowler.