I'm running an IP5000, 40C, and two Active Reactor 5000, 40C. Lots of people are running SMC 5000 50C and they seem to be great.
The Active Reactor from Dandenong is a great battery also, and it's cheap. hence me having 2.
Like the nim's, they do go off a bit over time. mine are not as potent as they were 18 months ago but I figure that's not a bad service life.
Cheers
-a