The interesting thing is not to look at the sales spike in the following weeks, it's to see if it gives the console any momentum. The goal of a price cut is not to get a spike...
However it will be pretty hard to visualize momentum before we get into 2008, since we're getting close to holiday season!
Me, I have no idea about the momentum this can give to the PS3... Probably not much, because the issue is still games, and 400 €/$ is not a mass market price yet.
As for the initial sales spike, I predict a 50%-150% increase in sales for Europe in the first week... Remember that:
1- It's not just a new gimped model, it's also a price cut on the starter pack (which
includes 2 games and controllers for 500 € from then on).
2- Some people will be scared at the announcement (probably better called "lie") that the 60 GB unit is discontinued and no BC will exist afterwards. (Way to respect your customers Sony...).
3- There are still some Sony fanboys who haven't bought the console in Europe due to its pricing. That's the kind of thing that contributes to a spike.
Does anyone think my scenario is too optimistic for the PS3?