Efficient has connotations of economy, of optimal use of resources but with a hint of parsimony - another way to get efficiency is to reduce the denominator.
Yep. A top fuel dragster goes from 0-60 mph (~0-100 kmh) in about 0.2 seconds, but it will use about 20 gallons (~75 liters) of fuel going 1,000 ft (~300 m). Very high performance. Very low efficiency.
The denominator is "resources," which here means "resource cost." Increasing resource cost reduces efficiency. You want to either increase the numerator ("performance") or decrease the denominator ("resources").
Performant emphasises the numerator much more.