If you feel comfortable overclocking the e2180 to its limits, get the e2180.
Otherwise, the 5000+ BE can do 3ghz easily on dirt cheap cooling (sub $15) and it is about $8-10 more expensive then the e2180. Factor in the cheaper motherboards on the am2 side (
Newegg.com - GIGABYTE GA-MA78G-DS3H AM2+/AM2 AMD 780G HDMI ATX AMD Motherboard - AMD Motherboards for example, can find cheaper), and you are talking about equal pricing between the two.
Personally, I would choose the 5000+ BE for the reason that I wouldn't want to pay the extra money to squeeze extra performance out of the e2180 (for cooling) which is already stressed.
If the e2180 can be overclocked to the same clocks as the 5000+ on the same cooling with no problem, then I will shut up and tell you to go with the e2180, lol. I don't think it can, however.