Things to consider for 3,1 Mac Pros:
- RAM is a lot more expensive, and DDR2
- First two PCI slots 1 & 2 are 2.0 (500MB/sec per lane), second two slots are 1.0 (250MB/sec per lane), so that handicap is to be taken into consideration.
From
Apple's website:
"
Mac Pro (Early 2008)
The Mac Pro (Early 2008) computers implement PCI Express revision 2.0 which support twice the data rate per lane as the PCI Express revision 1. Slots 1 and 2 are both x16 revision 2.0 slots. Slots 3 and 4 are both x4 revision 1 slots. Placing a revision 1 card in a revision 2.0 slot, or visa-versa, is supported and results in a revision 1 link.
The number of lanes for each of these slots is permanently set for the Mac Pro (Early 2008). The Expansion Slot Utility doesn't apply.
Mac Pro (Early 2009) and Mac Pro (Mid 2010)
The Mac Pro (Early 2009) and Mac Pro (Mid 2010) computers implement PCI Express revision 2.0 for all four slots. Slots 1 and 2 are x16 slots, and slots 3 and 4 are x4 slots. As with the Mac Pro (Early 2008), placing a revision 1 card in a revision 2.0 slot works and results in a revision 1 link.
The Expansion Slot Utility is not required for these configurations, since the number of lanes for each slot are permanently set."
What they don't mention is that there are only 36 lanes available to the PCI slots, and therefore slots 3 & 4 are switched, meaning they share x4 lanes between the two of them. Credit for this discovery goes to Nanofrog, who was looking up part numbers which revealed the PCI switch.
Lastly, the 4,1 and 5,1 Mac Pros can use 6-core CPUs, whereas the 3,1 cannot. In a 4,1 like mine, you need to change the firmware to 5,1 to allow this, but otherwise they are the same machine physically.