http://ciisqbg45nggykdl6rjdrq3wc64csga4vkphu66qsi65mypeitqedoad.onion/blog/which-config-to-use
The default ECC configs use the elliptic curve secp521r1, which is 521-bit, or according to https://web.archive.org/web/20090207194412/http://www.nsa.gov/business/programs/elliptic_curve.shtml roughly the same as 15360-bit RSA, or a security level (symmetric key size) of 256-bits.