I know this has been asked and answered many times over in various threads, but I'm in a bind and will have to make a quick purcahse decision (today or tomorrow) so hopefully you'll forgive me for asking it again?

((btw, if anyone knows of a great thread that discusses this, could you please link?))
Bottom line, my trusty old MacPro 3,1 is dying - quickly - and I want to replace it with a silver tower MacPro (no dustbins, please) that will be cpu-upgradeable, later when I get the funds.
I know there have been many models (4,1's and 5,1's) discussed here as good/great upgradeable candidates, but if you have to pick one today, which one would it be?
many thanks for your answers and time.