i would say go for blackice.

i've bought a blackice I extreme once,
friend of mine is still using him and his temps are realy good.

just a personal feeling.
somebody has some experience with alphacool?

I once had the Airplex EVO 340, that was big fun.

I think performance wise there will not be much difference.

performance wise they are practically the same - I have had them both.
but I would go for the evo240 because:
1. the paint stay on it, just put a BI on a table and see what I mean.
2. It is much easier to put your screws in the evo because they use european standards as opposed to the BI who use the american standard.

just my 2 cents