No. Efficiency hardly matters on a PSU. On your system you'd be hardly saving anything going with a few % higher efficiency (under €5 a year, likely).
What is more important is the quality of the PSU. It will affect longevity of all parts aswell as itself, and affects reliability (crashes, problems).
Don't go for the corsair cx550. It hasn't been reviewed so all we know it could be dangerous, and low quality.
Go for the CX450M (modular version) which has been proffesionals reviewed and proven great value.