In my experience, where you run into the real problem is that the BIOS of the motherboard won't have the microcode patch for a bigger / better / newer processor.
Even if you did get a newer CPU to boot, it would only have the capabilities of the older CPU - you would be limiting the new one artificially, and it would be no better than sticking with the old one. Possibly worse, since it may very well not boot at all.
Very unlikely. Seems the server supports 533Mhz FSB only.