One advantage that the Sauber guys will have is that they will have knowlege of the Ferarri style installation as they ran Ferarri engines as Petronas engines before BMW took over.
I have a feeling that Sauber will be using the year old engines that STR used this year, making their installation a 2 year old power train i think, as STR will be running the Ferarri 056s that Ferarri are using this year. STR last year were used as a development bed by Ferarri for their engines they year, hence why they had simmilar performance to the Ferarri towards the end of 08 and better performance than the Red Bull last year.
I think they have chosen rightly with their engine. Could be that the engine breakdown is as follows for 2010; Mercedes - 3 (Brawn, Force India & McLaren), Ferarri - 3 (Ferarri, STR & Sauber), Renault - 3 (Renault, Red Bull & Williams) Toyota - 1 (Toyota), Cosworth - 4 (Manor, Campos, Lotus & USF1)
Although i feel that one team will not make it for 2010, i think it could be a team like Campos or even Toyota, as those are my 2 faverouite teams for not making the 2010 grid, altho somthing says to me that it could be Campos if reports are to be belived.