Thanks for your comments.
It looks like we have a split decision (50/50).
I spent some time looking for the heat/fan specs but haven't found them.
Even though the 4800 uses more power, its temperture ratio is narrower and fits into the 3800.
Logic tells me that it should support it, but on the other hand the 4800 have 2 cores in one and should tend to heat more. Right?
Size wise they should be the same, too.