Considerations, in general.
(a) what the OEM documents might say
(b) drift down generally will be to a higher level than climb to, depending on turbulence
(c) a bit of turbulence and you can probably say goodbye to the altitude pad you might have started out with
(d) subject to (a), I can't see very much wrong with using the OEI climb to data as the basis for terrain clearance planning, again subject to turbulence ... significant turbulence and the bets become increasingly airy fairy ... ie better plan is to get away from seriously high terrain as an early immediate action post failure ..