Length

Symmetric Key	EC	RSA	Time to Break	Machines	Memory
56	112	430	< 5 min	105	trivial
80	160	760	600 months	4300	4Gb
96	192	1020	3*10^6 yrs	114	170Gb
128	256	1620	10^16 yrs	0.16	120Tb

Analysis by RSA-labs [1]

Symmetric	EC	Mod Discrete Log field	Discrete Log Subgroup
80	160	1024	160
112	224	2048	224
128	256	3072	256
192	384	7680	384
256	512	15360	512

NESSIE recommendations [1]

RSA Keysize	Lifetime
512	1 hour
576	10 hours
640	4 days
704	30 days
796	8 months
1024	1 year

IETF 2004 [2]

[1] ECRYPT II 2011 ​http://www.ecrypt.eu.org/documents/D.SPA.17.pdf
[2] ​http://www.ietf.org/internet-drafts/draft-ietf-msec-ipsec-signatures-03.txt