Well I doubt Sauber would have much say in the matter if Ferrari wanted Perez, since firstly they supply their engines and secondly, as Perez is part of the Ferrari young driver program I'd imagine he'd have an option in his contract for Ferrari so that if and when they want him, they get him.
I would like to point out that I posted that link before the race, so these Perez to Sauber rumours weren't based on his performance today, though obviously it will enhance the rumours.
That said, I don't think he should go to Ferrari this year if they do want him, I think he should stay at Sauber this year continuing to develop and then go to Ferrari next year if he can. As you said, he'd be under a lot of pressure in an under-performing Ferrari that he'll have to learn without any testing.