Seeing that Saubers are running Ferrari engines which are only a few races back in evolution from the actual units run by Ferrari team, and are still struggling, BMW engines at the back of the Sauber will likely not make them much faster in 2006. Good thing is that with BMW buying over Sauber, there's more $$$ around as they dont have to spend on customer engines and investment by BMW goes to the wind tunnel development. I just hope that the engineers, aerodynamicst, technical director is up to the mark to bring them to the front. Took famed technical directors like Geof Willis (BAR ex Williams) and Mike Gascoyne (Toyota ex Renault) 1 complete season to make a difference when they switched teams.
My guess is that BMW Team will take at least 1 season to be really competitive in the front line when they start racing in 2006.