I'm playing a BBn1/Clr9 right now, and having a lot of fun. Str. and Luck domains (cleric of Kord - seemed a natch). It's annoying to be a caster level behind, but I can enlarge (from str domain), plus the cleric buffs, and do well most of the time, rage when I have to (which isn't much), and rally knock down some foes. In this campaign, I can use the uber-broken persistent spell. Woot!
I don't think an even level split would be as powerful. I'd go either cleric3/bbnx, or bbn1/clericx. Losing caster levels really sucks.