I think in this rare case, Google translate provides a spot-on translation. I would translate the whole sentence as
> We should forget about small efficiencies, say about 97% of the time: premature optimization is the root of all evil.
> 97%
_Translation notes:_ I just translated "say about" as . The "say" here should really be something like or, as Hyperworm suggested, , but I thought that the resulting tone would be a bit too conversational, which is not really the case in English.